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 $176.33   13.255%   $199.7025   $199.70   $199.70   $199.70  
  Purchase #2 $41.85   6.232%   $44.4581   $44.46   $44.45   $44.50  
  Purchase #3 $59.80   6.827%   $63.8825   $63.88   $63.90   $63.90  
  Purchase #4 $40.35   7.420%   $43.344   $43.34   $43.35   $43.30  
  Purchase #5 $126.81   7.785%   $136.6822   $136.68   $136.70   $136.70  
  Purchase #6 $104.38   6.292%   $110.9476   $110.95   $110.95   $110.90  
  Purchase #7 $226.68   12.319%   $254.6047   $254.60   $254.60   $254.60  
  7 purchase totals = $776.20       $853.6216   $853.61   $853.65   $853.60