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 $194.61   6.119%   $206.5182   $206.52   $206.50   $206.50  
  Purchase #2 $31.98   9.155%   $34.9078   $34.91   $34.90   $34.90  
  Purchase #3 $32.91   7.294%   $35.3105   $35.31   $35.30   $35.30  
  Purchase #4 $191.53   5.226%   $201.5394   $201.54   $201.55   $201.50  
  Purchase #5 $125.97   11.356%   $140.2752   $140.28   $140.30   $140.30  
  Purchase #6 $173.99   8.501%   $188.7809   $188.78   $188.80   $188.80  
  Purchase #7 $13.28   10.466%   $14.6699   $14.67   $14.65   $14.70  
  7 purchase totals = $764.27       $822.0019   $822.01   $822.00   $822.00