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 $72.28   13.437%   $81.9923   $81.99   $82.00   $82.00  
  Purchase #2 $106.53   11.627%   $118.9162   $118.92   $118.90   $118.90  
  Purchase #3 $14.99   13.254%   $16.9768   $16.98   $17.00   $17.00  
  Purchase #4 $127.62   13.232%   $144.5067   $144.51   $144.50   $144.50  
  Purchase #5 $59.59   7.664%   $64.157   $64.16   $64.15   $64.20  
  Purchase #6 $204.39   10.687%   $226.2332   $226.23   $226.25   $226.20  
  Purchase #7 $222.52   12.286%   $249.8588   $249.86   $249.85   $249.90  
  7 purchase totals = $807.92       $902.6410   $902.65   $902.65   $902.70