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 $60.68   9.810%   $66.6327   $66.63   $66.65   $66.60  
  Purchase #2 $241.82   8.392%   $262.1135   $262.11   $262.10   $262.10  
  Purchase #3 $202.77   12.856%   $228.8381   $228.84   $228.85   $228.80  
  Purchase #4 $248.43   13.662%   $282.3705   $282.37   $282.35   $282.40  
  Purchase #5 $212.86   8.582%   $231.1276   $231.13   $231.15   $231.10  
  Purchase #6 $111.84   3.205%   $115.4245   $115.42   $115.40   $115.40  
  Purchase #7 $39.55   12.465%   $44.4799   $44.48   $44.50   $44.50  
  7 purchase totals = $1,117.95       $1,230.9868   $1,230.98   $1,231.00   $1,230.90