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 $59.60   3.659%   $61.7808   $61.78   $61.80   $61.80  
  Purchase #2 $95.45   3.325%   $98.6237   $98.62   $98.60   $98.60  
  Purchase #3 $104.31   3.287%   $107.7387   $107.74   $107.75   $107.70  
  Purchase #4 $144.92   11.174%   $161.1134   $161.11   $161.10   $161.10  
  Purchase #5 $204.90   7.442%   $220.1487   $220.15   $220.15   $220.10  
  Purchase #6 $68.79   6.853%   $73.5042   $73.50   $73.50   $73.50  
  Purchase #7 $142.51   7.699%   $153.4818   $153.48   $153.50   $153.50  
  7 purchase totals = $820.48       $876.3913   $876.38   $876.40   $876.30