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 $88.48   4.403%   $92.3758   $92.38   $92.40   $92.40  
  Purchase #2 $114.49   3.809%   $118.8509   $118.85   $118.85   $118.90  
  Purchase #3 $119.53   9.452%   $130.828   $130.83   $130.85   $130.80  
  Purchase #4 $26.59   3.354%   $27.4818   $27.48   $27.50   $27.50  
  Purchase #5 $133.39   8.844%   $145.187   $145.19   $145.20   $145.20  
  Purchase #6 $126.66   7.359%   $135.9809   $135.98   $136.00   $136.00  
  Purchase #7 $140.30   9.149%   $153.136   $153.14   $153.15   $153.10  
  7 purchase totals = $749.44       $803.8404   $803.85   $803.95   $803.90