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 $213.91   3.676%   $221.7733   $221.77   $221.75   $221.80  
  Purchase #2 $248.99   6.411%   $264.9527   $264.95   $264.95   $265.00  
  Purchase #3 $6.92   5.199%   $7.2798   $7.28   $7.30   $7.30  
  Purchase #4 $56.35   5.621%   $59.5174   $59.52   $59.50   $59.50  
  Purchase #5 $75.69   11.351%   $84.2816   $84.28   $84.30   $84.30  
  Purchase #6 $235.42   6.168%   $249.9407   $249.94   $249.95   $249.90  
  Purchase #7 $55.91   6.549%   $59.5715   $59.57   $59.55   $59.60  
  7 purchase totals = $893.19       $947.3170   $947.31   $947.30   $947.40