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 $55.72   13.291%   $63.1257   $63.13   $63.15   $63.10  
  Purchase #2 $66.28   8.165%   $71.6918   $71.69   $71.70   $71.70  
  Purchase #3 $174.40   11.862%   $195.0873   $195.09   $195.10   $195.10  
  Purchase #4 $156.49   3.139%   $161.4022   $161.40   $161.40   $161.40  
  Purchase #5 $148.65   10.832%   $164.7518   $164.75   $164.75   $164.80  
  Purchase #6 $232.78   5.861%   $246.4232   $246.42   $246.40   $246.40  
  Purchase #7 $39.94   10.204%   $44.0155   $44.02   $44.00   $44.00  
  7 purchase totals = $874.26       $946.4975   $946.50   $946.50   $946.50