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 $47.33   12.711%   $53.3461   $53.35   $53.35   $53.30  
  Purchase #2 $225.94   9.566%   $247.5534   $247.55   $247.55   $247.60  
  Purchase #3 $204.95   7.133%   $219.5691   $219.57   $219.55   $219.60  
  Purchase #4 $71.79   8.763%   $78.081   $78.08   $78.10   $78.10  
  Purchase #5 $164.94   5.269%   $173.6307   $173.63   $173.65   $173.60  
  Purchase #6 $11.94   6.459%   $12.7112   $12.71   $12.70   $12.70  
  Purchase #7 $90.76   10.245%   $100.0584   $100.06   $100.05   $100.10  
  7 purchase totals = $817.65       $884.9499   $884.95   $884.95   $885.00