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 $90.27   4.130%   $93.9982   $94.00   $94.00   $94.00  
  Purchase #2 $111.87   10.254%   $123.3411   $123.34   $123.35   $123.30  
  Purchase #3 $53.43   12.275%   $59.9885   $59.99   $60.00   $60.00  
  Purchase #4 $225.68   5.291%   $237.6207   $237.62   $237.60   $237.60  
  Purchase #5 $168.36   7.712%   $181.3439   $181.34   $181.35   $181.30  
  Purchase #6 $141.38   13.162%   $159.9884   $159.99   $160.00   $160.00  
  Purchase #7 $173.45   12.607%   $195.3168   $195.32   $195.30   $195.30  
  7 purchase totals = $964.44       $1,051.5976   $1,051.60   $1,051.60   $1,051.50