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 $208.37   12.603%   $234.6309   $234.63   $234.65   $234.60  
  Purchase #2 $170.95   4.297%   $178.2957   $178.30   $178.30   $178.30  
  Purchase #3 $137.48   6.495%   $146.4093   $146.41   $146.40   $146.40  
  Purchase #4 $242.64   11.603%   $270.7935   $270.79   $270.80   $270.80  
  Purchase #5 $88.30   9.130%   $96.3618   $96.36   $96.35   $96.40  
  Purchase #6 $159.66   8.488%   $173.2119   $173.21   $173.20   $173.20  
  Purchase #7 $143.34   6.397%   $152.5095   $152.51   $152.50   $152.50  
  7 purchase totals = $1,150.74       $1,252.2126   $1,252.21   $1,252.20   $1,252.20