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 $68.86   9.665%   $75.5153   $75.52   $75.50   $75.50  
  Purchase #2 $126.59   9.247%   $138.2958   $138.30   $138.30   $138.30  
  Purchase #3 $68.36   12.224%   $76.7163   $76.72   $76.70   $76.70  
  Purchase #4 $77.34   11.160%   $85.9711   $85.97   $85.95   $86.00  
  Purchase #5 $238.65   10.293%   $263.2142   $263.21   $263.20   $263.20  
  Purchase #6 $109.80   6.196%   $116.6032   $116.60   $116.60   $116.60  
  Purchase #7 $57.33   9.371%   $62.7024   $62.70   $62.70   $62.70  
  7 purchase totals = $746.93       $819.0183   $819.02   $818.95   $819.00