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 $48.67   8.824%   $52.9646   $52.96   $52.95   $53.00  
  Purchase #2 $117.99   10.241%   $130.0734   $130.07   $130.05   $130.10  
  Purchase #3 $46.47   6.427%   $49.4566   $49.46   $49.45   $49.50  
  Purchase #4 $33.67   11.219%   $37.4474   $37.45   $37.45   $37.40  
  Purchase #5 $208.47   4.125%   $217.0694   $217.07   $217.05   $217.10  
  Purchase #6 $194.53   11.155%   $216.2298   $216.23   $216.25   $216.20  
  Purchase #7 $116.73   5.244%   $122.8513   $122.85   $122.85   $122.90  
  7 purchase totals = $766.53       $826.0925   $826.09   $826.05   $826.20