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 $158.36   5.310%   $166.7689   $166.77   $166.75   $166.80  
  Purchase #2 $188.69   3.679%   $195.6319   $195.63   $195.65   $195.60  
  Purchase #3 $230.68   3.559%   $238.8899   $238.89   $238.90   $238.90  
  Purchase #4 $123.35   3.306%   $127.428   $127.43   $127.45   $127.40  
  Purchase #5 $232.73   6.571%   $248.0227   $248.02   $248.00   $248.00  
  Purchase #6 $163.86   4.821%   $171.7597   $171.76   $171.75   $171.80  
  Purchase #7 $177.36   3.735%   $183.9844   $183.98   $184.00   $184.00  
  7 purchase totals = $1,275.03       $1,332.4855   $1,332.48   $1,332.50   $1,332.50