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 $47.97   8.332%   $51.9669   $51.97   $51.95   $52.00  
  Purchase #2 $229.28   11.284%   $255.152   $255.15   $255.15   $255.20  
  Purchase #3 $32.34   3.598%   $33.5036   $33.50   $33.50   $33.50  
  Purchase #4 $188.91   4.692%   $197.7737   $197.77   $197.75   $197.80  
  Purchase #5 $88.88   8.245%   $96.2082   $96.21   $96.20   $96.20  
  Purchase #6 $68.27   13.758%   $77.6626   $77.66   $77.65   $77.70  
  Purchase #7 $217.50   13.286%   $246.3971   $246.40   $246.40   $246.40  
  7 purchase totals = $873.15       $958.6641   $958.66   $958.60   $958.80