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 $118.81   6.669%   $126.7334   $126.73   $126.75   $126.70  
  Purchase #2 $31.52   11.415%   $35.118   $35.12   $35.10   $35.10  
  Purchase #3 $230.84   6.582%   $246.0339   $246.03   $246.05   $246.00  
  Purchase #4 $43.51   6.603%   $46.383   $46.38   $46.40   $46.40  
  Purchase #5 $175.96   10.380%   $194.2246   $194.22   $194.20   $194.20  
  Purchase #6 $57.76   5.172%   $60.7473   $60.75   $60.75   $60.70  
  Purchase #7 $177.94   3.369%   $183.9348   $183.93   $183.95   $183.90  
  7 purchase totals = $836.34       $893.1750   $893.16   $893.20   $893.00