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 $28.91   13.320%   $32.7608   $32.76   $32.75   $32.80  
  Purchase #2 $182.47   6.821%   $194.9163   $194.92   $194.90   $194.90  
  Purchase #3 $79.44   8.280%   $86.0176   $86.02   $86.00   $86.00  
  Purchase #4 $244.35   13.772%   $278.0019   $278.00   $278.00   $278.00  
  Purchase #5 $94.31   8.753%   $102.565   $102.57   $102.55   $102.60  
  Purchase #6 $25.69   5.679%   $27.1489   $27.15   $27.15   $27.10  
  Purchase #7 $124.75   13.162%   $141.1696   $141.17   $141.15   $141.20  
  7 purchase totals = $779.92       $862.5801   $862.59   $862.50   $862.60