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 $146.76   10.224%   $161.7647   $161.76   $161.75   $161.80  
  Purchase #2 $228.94   3.376%   $236.669   $236.67   $236.65   $236.70  
  Purchase #3 $77.97   4.525%   $81.4981   $81.50   $81.50   $81.50  
  Purchase #4 $205.73   9.546%   $225.369   $225.37   $225.35   $225.40  
  Purchase #5 $58.62   9.430%   $64.1479   $64.15   $64.15   $64.10  
  Purchase #6 $62.39   10.690%   $69.0595   $69.06   $69.05   $69.10  
  Purchase #7 $20.78   11.731%   $23.2177   $23.22   $23.20   $23.20  
  7 purchase totals = $801.19       $861.7259   $861.73   $861.65   $861.80