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 $54.95   12.778%   $61.9715   $61.97   $61.95   $62.00  
  Purchase #2 $185.66   7.541%   $199.6606   $199.66   $199.65   $199.70  
  Purchase #3 $233.55   4.189%   $243.3334   $243.33   $243.35   $243.30  
  Purchase #4 $135.75   7.836%   $146.3874   $146.39   $146.40   $146.40  
  Purchase #5 $106.65   11.150%   $118.5415   $118.54   $118.55   $118.50  
  Purchase #6 $148.79   5.526%   $157.0121   $157.01   $157.00   $157.00  
  Purchase #7 $50.52   8.460%   $54.794   $54.79   $54.80   $54.80  
  7 purchase totals = $915.87       $981.7005   $981.69   $981.70   $981.70