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 $147.32   8.146%   $159.3207   $159.32   $159.30   $159.30  
  Purchase #2 $67.91   12.864%   $76.6459   $76.65   $76.65   $76.60  
  Purchase #3 $119.49   8.543%   $129.698   $129.70   $129.70   $129.70  
  Purchase #4 $219.80   4.132%   $228.8821   $228.88   $228.90   $228.90  
  Purchase #5 $237.47   6.799%   $253.6156   $253.62   $253.60   $253.60  
  Purchase #6 $210.71   10.186%   $232.1729   $232.17   $232.15   $232.20  
  Purchase #7 $174.54   10.113%   $192.1912   $192.19   $192.20   $192.20  
  7 purchase totals = $1,177.24       $1,272.5264   $1,272.53   $1,272.50   $1,272.50