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 $88.59   6.268%   $94.1428   $94.14   $94.15   $94.10  
  Purchase #2 $95.42   8.502%   $103.5326   $103.53   $103.55   $103.50  
  Purchase #3 $218.75   11.738%   $244.4269   $244.43   $244.45   $244.40  
  Purchase #4 $171.26   5.465%   $180.6194   $180.62   $180.60   $180.60  
  Purchase #5 $125.25   13.313%   $141.9245   $141.92   $141.90   $141.90  
  Purchase #6 $231.72   3.571%   $239.9947   $239.99   $240.00   $240.00  
  Purchase #7 $237.58   4.311%   $247.8221   $247.82   $247.80   $247.80  
  7 purchase totals = $1,168.57       $1,252.4630   $1,252.45   $1,252.45   $1,252.30