Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $153.78   7.862%   $165.8702   $165.87   $165.85   $165.90  
  Purchase #2 $213.91   10.409%   $236.1759   $236.18   $236.20   $236.20  
  Purchase #3 $151.88   9.558%   $166.3967   $166.40   $166.40   $166.40  
  Purchase #4 $181.37   9.732%   $199.0209   $199.02   $199.00   $199.00  
  Purchase #5 $237.98   7.180%   $255.067   $255.07   $255.05   $255.10  
  Purchase #6 $244.34   12.239%   $274.2448   $274.24   $274.25   $274.20  
  Purchase #7 $158.62   8.458%   $172.0361   $172.04   $172.05   $172.00  
  7 purchase totals = $1,341.88       $1,468.8116   $1,468.82   $1,468.80   $1,468.80