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 $112.80   7.700%   $121.4856   $121.49   $121.50   $121.50  
  Purchase #2 $191.66   11.692%   $214.0689   $214.07   $214.05   $214.10  
  Purchase #3 $101.31   13.624%   $115.1125   $115.11   $115.10   $115.10  
  Purchase #4 $148.85   12.352%   $167.236   $167.24   $167.25   $167.20  
  Purchase #5 $65.73   3.739%   $68.1876   $68.19   $68.20   $68.20  
  Purchase #6 $150.93   12.338%   $169.5517   $169.55   $169.55   $169.60  
  Purchase #7 $129.56   3.501%   $134.0959   $134.10   $134.10   $134.10  
  7 purchase totals = $900.84       $989.7382   $989.75   $989.75   $989.80