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 $63.54   7.613%   $68.3773   $68.38   $68.40   $68.40  
  Purchase #2 $164.96   12.632%   $185.7977   $185.80   $185.80   $185.80  
  Purchase #3 $94.41   9.460%   $103.3412   $103.34   $103.35   $103.30  
  Purchase #4 $21.44   13.116%   $24.2521   $24.25   $24.25   $24.30  
  Purchase #5 $121.85   13.106%   $137.8197   $137.82   $137.80   $137.80  
  Purchase #6 $211.88   9.487%   $231.9811   $231.98   $232.00   $232.00  
  Purchase #7 $245.64   5.554%   $259.2828   $259.28   $259.30   $259.30  
  7 purchase totals = $923.72       $1,010.8519   $1,010.85   $1,010.90   $1,010.90