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 $39.89   11.367%   $44.4243   $44.42   $44.40   $44.40  
  Purchase #2 $171.94   9.397%   $188.0972   $188.10   $188.10   $188.10  
  Purchase #3 $108.29   9.577%   $118.6609   $118.66   $118.65   $118.70  
  Purchase #4 $109.25   4.543%   $114.2132   $114.21   $114.20   $114.20  
  Purchase #5 $85.71   3.108%   $88.3739   $88.37   $88.35   $88.40  
  Purchase #6 $237.81   4.182%   $247.7552   $247.76   $247.75   $247.80  
  Purchase #7 $70.85   8.251%   $76.6958   $76.70   $76.70   $76.70  
  7 purchase totals = $823.74       $878.2205   $878.22   $878.15   $878.30