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 $29.81   10.546%   $32.9538   $32.95   $32.95   $33.00  
  Purchase #2 $145.38   13.484%   $164.983   $164.98   $165.00   $165.00  
  Purchase #3 $159.78   10.312%   $176.2565   $176.26   $176.25   $176.30  
  Purchase #4 $233.39   4.639%   $244.217   $244.22   $244.20   $244.20  
  Purchase #5 $91.71   4.793%   $96.1057   $96.11   $96.10   $96.10  
  Purchase #6 $116.91   8.718%   $127.1022   $127.10   $127.10   $127.10  
  Purchase #7 $158.57   11.394%   $176.6375   $176.64   $176.65   $176.60  
  7 purchase totals = $935.55       $1,018.2557   $1,018.26   $1,018.25   $1,018.30