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 $241.60   6.626%   $257.6084   $257.61   $257.60   $257.60  
  Purchase #2 $132.66   12.812%   $149.6564   $149.66   $149.65   $149.70  
  Purchase #3 $180.59   6.576%   $192.4656   $192.47   $192.45   $192.50  
  Purchase #4 $80.59   4.486%   $84.2053   $84.21   $84.20   $84.20  
  Purchase #5 $203.96   12.105%   $228.6494   $228.65   $228.65   $228.60  
  Purchase #6 $200.33   6.726%   $213.8042   $213.80   $213.80   $213.80  
  Purchase #7 $69.45   10.868%   $76.9978   $77.00   $77.00   $77.00  
  7 purchase totals = $1,109.18       $1,203.3871   $1,203.40   $1,203.35   $1,203.40