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 $111.27   7.211%   $119.2937   $119.29   $119.30   $119.30  
  Purchase #2 $180.56   6.308%   $191.9497   $191.95   $191.95   $191.90  
  Purchase #3 $92.97   9.802%   $102.0829   $102.08   $102.10   $102.10  
  Purchase #4 $69.88   8.265%   $75.6556   $75.66   $75.65   $75.70  
  Purchase #5 $174.78   5.340%   $184.1133   $184.11   $184.10   $184.10  
  Purchase #6 $63.25   11.330%   $70.4162   $70.42   $70.40   $70.40  
  Purchase #7 $183.49   8.166%   $198.4738   $198.47   $198.45   $198.50  
  7 purchase totals = $876.20       $941.9852   $941.98   $941.95   $942.00