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 $84.70   5.620%   $89.4601   $89.46   $89.45   $89.50  
  Purchase #2 $113.52   3.394%   $117.3729   $117.37   $117.35   $117.40  
  Purchase #3 $206.53   10.759%   $228.7506   $228.75   $228.75   $228.80  
  Purchase #4 $23.68   8.255%   $25.6348   $25.63   $25.65   $25.60  
  Purchase #5 $27.65   10.831%   $30.6448   $30.64   $30.65   $30.60  
  Purchase #6 $12.73   10.363%   $14.0492   $14.05   $14.05   $14.00  
  Purchase #7 $212.86   13.228%   $241.0171   $241.02   $241.00   $241.00  
  7 purchase totals = $681.67       $746.9295   $746.92   $746.90   $746.90