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 $148.62   10.179%   $163.748   $163.75   $163.75   $163.70  
  Purchase #2 $153.98   12.305%   $172.9272   $172.93   $172.95   $172.90  
  Purchase #3 $81.41   8.685%   $88.4805   $88.48   $88.50   $88.50  
  Purchase #4 $140.68   3.144%   $145.103   $145.10   $145.10   $145.10  
  Purchase #5 $23.25   7.670%   $25.0333   $25.03   $25.05   $25.00  
  Purchase #6 $195.51   5.689%   $206.6326   $206.63   $206.65   $206.60  
  Purchase #7 $13.35   12.663%   $15.0405   $15.04   $15.05   $15.00  
  7 purchase totals = $756.80       $816.9651   $816.96   $817.05   $816.80