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 $120.74   4.293%   $125.9234   $125.92   $125.90   $125.90  
  Purchase #2 $75.50   11.646%   $84.2927   $84.29   $84.30   $84.30  
  Purchase #3 $13.35   8.285%   $14.456   $14.46   $14.45   $14.50  
  Purchase #4 $219.54   11.455%   $244.6883   $244.69   $244.70   $244.70  
  Purchase #5 $150.30   7.545%   $161.6401   $161.64   $161.65   $161.60  
  Purchase #6 $172.81   11.688%   $193.008   $193.01   $193.00   $193.00  
  Purchase #7 $38.54   6.368%   $40.9942   $40.99   $41.00   $41.00  
  7 purchase totals = $790.78       $865.0027   $865.00   $865.00   $865.00