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 $54.49   7.143%   $58.3822   $58.38   $58.40   $58.40  
  Purchase #2 $103.66   3.581%   $107.3721   $107.37   $107.35   $107.40  
  Purchase #3 $213.94   10.591%   $236.5984   $236.60   $236.60   $236.60  
  Purchase #4 $94.88   8.368%   $102.8196   $102.82   $102.80   $102.80  
  Purchase #5 $106.35   11.114%   $118.1697   $118.17   $118.15   $118.20  
  Purchase #6 $211.63   6.175%   $224.6982   $224.70   $224.70   $224.70  
  Purchase #7 $196.68   3.579%   $203.7192   $203.72   $203.70   $203.70  
  7 purchase totals = $981.63       $1,051.7594   $1,051.76   $1,051.70   $1,051.80