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 $131.79   6.532%   $140.3985   $140.40   $140.40   $140.40  
  Purchase #2 $214.26   8.282%   $232.005   $232.01   $232.00   $232.00  
  Purchase #3 $60.91   13.291%   $69.0055   $69.01   $69.00   $69.00  
  Purchase #4 $167.70   12.290%   $188.3103   $188.31   $188.30   $188.30  
  Purchase #5 $175.47   6.172%   $186.3   $186.30   $186.30   $186.30  
  Purchase #6 $98.53   12.613%   $110.9576   $110.96   $110.95   $111.00  
  Purchase #7 $240.45   6.383%   $255.7979   $255.80   $255.80   $255.80  
  7 purchase totals = $1,089.11       $1,182.7748   $1,182.79   $1,182.75   $1,182.80