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 $50.92   5.476%   $53.7084   $53.71   $53.70   $53.70  
  Purchase #2 $219.74   13.428%   $249.2467   $249.25   $249.25   $249.20  
  Purchase #3 $43.28   11.474%   $48.2459   $48.25   $48.25   $48.20  
  Purchase #4 $208.46   8.647%   $226.4855   $226.49   $226.50   $226.50  
  Purchase #5 $15.90   9.174%   $17.3587   $17.36   $17.35   $17.40  
  Purchase #6 $113.52   8.678%   $123.3713   $123.37   $123.35   $123.40  
  Purchase #7 $46.54   6.126%   $49.391   $49.39   $49.40   $49.40  
  7 purchase totals = $698.36       $767.8075   $767.82   $767.80   $767.80