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 $220.60   3.223%   $227.7099   $227.71   $227.70   $227.70  
  Purchase #2 $58.74   4.239%   $61.23   $61.23   $61.25   $61.20  
  Purchase #3 $216.72   3.171%   $223.5922   $223.59   $223.60   $223.60  
  Purchase #4 $92.39   12.783%   $104.2002   $104.20   $104.20   $104.20  
  Purchase #5 $19.26   5.557%   $20.3303   $20.33   $20.35   $20.30  
  Purchase #6 $206.95   6.548%   $220.5011   $220.50   $220.50   $220.50  
  Purchase #7 $136.66   3.291%   $141.1575   $141.16   $141.15   $141.20  
  7 purchase totals = $951.32       $998.7212   $998.72   $998.75   $998.70