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 $47.27   12.658%   $53.2534   $53.25   $53.25   $53.30  
  Purchase #2 $151.57   11.193%   $168.5352   $168.54   $168.55   $168.50  
  Purchase #3 $156.29   4.625%   $163.5184   $163.52   $163.50   $163.50  
  Purchase #4 $197.30   9.686%   $216.4105   $216.41   $216.40   $216.40  
  Purchase #5 $83.91   10.795%   $92.9681   $92.97   $92.95   $93.00  
  Purchase #6 $153.61   9.361%   $167.9894   $167.99   $168.00   $168.00  
  Purchase #7 $54.92   10.708%   $60.8008   $60.80   $60.80   $60.80  
  7 purchase totals = $844.87       $923.4758   $923.48   $923.45   $923.50