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 $63.62   7.288%   $68.2566   $68.26   $68.25   $68.30  
  Purchase #2 $53.51   13.309%   $60.6316   $60.63   $60.65   $60.60  
  Purchase #3 $133.89   9.231%   $146.2494   $146.25   $146.25   $146.20  
  Purchase #4 $216.98   5.145%   $228.1436   $228.14   $228.15   $228.10  
  Purchase #5 $144.75   8.299%   $156.7628   $156.76   $156.75   $156.80  
  Purchase #6 $200.28   6.578%   $213.4544   $213.45   $213.45   $213.50  
  Purchase #7 $144.49   4.731%   $151.3258   $151.33   $151.35   $151.30  
  7 purchase totals = $957.52       $1,024.8242   $1,024.82   $1,024.85   $1,024.80