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 $83.97   13.674%   $95.4521   $95.45   $95.45   $95.50  
  Purchase #2 $89.52   4.454%   $93.5072   $93.51   $93.50   $93.50  
  Purchase #3 $24.47   6.652%   $26.0977   $26.10   $26.10   $26.10  
  Purchase #4 $196.39   12.503%   $220.9446   $220.94   $220.95   $220.90  
  Purchase #5 $5.45   12.239%   $6.117   $6.12   $6.10   $6.10  
  Purchase #6 $182.51   10.347%   $201.3943   $201.39   $201.40   $201.40  
  Purchase #7 $84.65   9.287%   $92.5114   $92.51   $92.50   $92.50  
  7 purchase totals = $666.96       $736.0243   $736.02   $736.00   $736.00