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 $44.53   13.759%   $50.6569   $50.66   $50.65   $50.70  
  Purchase #2 $53.33   3.128%   $54.9982   $55.00   $55.00   $55.00  
  Purchase #3 $98.54   3.302%   $101.7938   $101.79   $101.80   $101.80  
  Purchase #4 $171.55   13.450%   $194.6235   $194.62   $194.60   $194.60  
  Purchase #5 $206.93   8.384%   $224.279   $224.28   $224.30   $224.30  
  Purchase #6 $209.83   7.837%   $226.2744   $226.27   $226.25   $226.30  
  Purchase #7 $94.97   6.218%   $100.8752   $100.88   $100.90   $100.90  
  7 purchase totals = $879.68       $953.5010   $953.50   $953.50   $953.60