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 $93.62   5.372%   $98.6493   $98.65   $98.65   $98.60  
  Purchase #2 $175.42   7.657%   $188.8519   $188.85   $188.85   $188.90  
  Purchase #3 $188.25   6.753%   $200.9625   $200.96   $200.95   $201.00  
  Purchase #4 $64.41   11.716%   $71.9563   $71.96   $71.95   $72.00  
  Purchase #5 $105.26   6.269%   $111.8587   $111.86   $111.85   $111.90  
  Purchase #6 $236.98   8.781%   $257.7892   $257.79   $257.80   $257.80  
  Purchase #7 $151.78   6.214%   $161.2116   $161.21   $161.20   $161.20  
  7 purchase totals = $1,015.72       $1,091.2795   $1,091.28   $1,091.25   $1,091.40