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 $139.34   8.414%   $151.0641   $151.06   $151.05   $151.10  
  Purchase #2 $68.44   7.252%   $73.4033   $73.40   $73.40   $73.40  
  Purchase #3 $221.31   9.242%   $241.7635   $241.76   $241.75   $241.80  
  Purchase #4 $205.49   5.863%   $217.5379   $217.54   $217.55   $217.50  
  Purchase #5 $206.27   4.370%   $215.284   $215.28   $215.30   $215.30  
  Purchase #6 $71.69   7.439%   $77.023   $77.02   $77.00   $77.00  
  Purchase #7 $153.86   11.446%   $171.4708   $171.47   $171.45   $171.50  
  7 purchase totals = $1,066.40       $1,147.5466   $1,147.53   $1,147.50   $1,147.60