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 $244.77   9.491%   $268.0011   $268.00   $268.00   $268.00  
  Purchase #2 $121.68   6.308%   $129.3556   $129.36   $129.35   $129.40  
  Purchase #3 $244.60   12.814%   $275.943   $275.94   $275.95   $275.90  
  Purchase #4 $175.66   4.496%   $183.5577   $183.56   $183.55   $183.60  
  Purchase #5 $211.37   10.135%   $232.7923   $232.79   $232.80   $232.80  
  Purchase #6 $219.33   13.162%   $248.1982   $248.20   $248.20   $248.20  
  Purchase #7 $89.34   5.489%   $94.2439   $94.24   $94.25   $94.20  
  7 purchase totals = $1,306.75       $1,432.0918   $1,432.09   $1,432.10   $1,432.10