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 $146.39   8.256%   $158.476   $158.48   $158.50   $158.50  
  Purchase #2 $185.54   13.845%   $211.228   $211.23   $211.25   $211.20  
  Purchase #3 $69.37   10.328%   $76.5345   $76.53   $76.55   $76.50  
  Purchase #4 $117.43   10.657%   $129.9445   $129.94   $129.95   $129.90  
  Purchase #5 $24.68   12.281%   $27.711   $27.71   $27.70   $27.70  
  Purchase #6 $227.65   8.843%   $247.7811   $247.78   $247.80   $247.80  
  Purchase #7 $147.90   12.357%   $166.176   $166.18   $166.20   $166.20  
  7 purchase totals = $918.96       $1,017.8511   $1,017.85   $1,017.95   $1,017.80