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 $203.41   12.372%   $228.5759   $228.58   $228.60   $228.60  
  Purchase #2 $31.83   7.267%   $34.1431   $34.14   $34.15   $34.10  
  Purchase #3 $111.42   12.847%   $125.7341   $125.73   $125.75   $125.70  
  Purchase #4 $54.54   6.641%   $58.162   $58.16   $58.15   $58.20  
  Purchase #5 $159.65   10.512%   $176.4324   $176.43   $176.45   $176.40  
  Purchase #6 $246.75   6.435%   $262.6284   $262.63   $262.65   $262.60  
  Purchase #7 $24.34   5.325%   $25.6361   $25.64   $25.65   $25.60  
  7 purchase totals = $831.94       $911.3120   $911.31   $911.40   $911.20