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 $83.96   11.739%   $93.8161   $93.82   $93.80   $93.80  
  Purchase #2 $235.47   11.630%   $262.8552   $262.86   $262.85   $262.90  
  Purchase #3 $151.57   9.276%   $165.6296   $165.63   $165.65   $165.60  
  Purchase #4 $236.70   11.326%   $263.5086   $263.51   $263.50   $263.50  
  Purchase #5 $166.84   13.237%   $188.9246   $188.92   $188.90   $188.90  
  Purchase #6 $232.95   9.647%   $255.4227   $255.42   $255.40   $255.40  
  Purchase #7 $113.43   8.145%   $122.6689   $122.67   $122.65   $122.70  
  7 purchase totals = $1,220.92       $1,352.8257   $1,352.83   $1,352.75   $1,352.80