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 $202.97   9.266%   $221.7772   $221.78   $221.80   $221.80  
  Purchase #2 $105.96   12.622%   $119.3343   $119.33   $119.35   $119.30  
  Purchase #3 $155.35   7.216%   $166.5601   $166.56   $166.55   $166.60  
  Purchase #4 $19.83   4.535%   $20.7293   $20.73   $20.75   $20.70  
  Purchase #5 $211.54   7.272%   $226.9232   $226.92   $226.90   $226.90  
  Purchase #6 $219.49   13.573%   $249.2814   $249.28   $249.30   $249.30  
  Purchase #7 $19.48   10.760%   $21.576   $21.58   $21.60   $21.60  
  7 purchase totals = $934.62       $1,026.1815   $1,026.18   $1,026.25   $1,026.20