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 $33.91   4.481%   $35.4295   $35.43   $35.45   $35.40  
  Purchase #2 $180.93   13.451%   $205.2669   $205.27   $205.25   $205.30  
  Purchase #3 $119.42   7.692%   $128.6058   $128.61   $128.60   $128.60  
  Purchase #4 $126.99   13.267%   $143.8378   $143.84   $143.85   $143.80  
  Purchase #5 $178.83   11.268%   $198.9806   $198.98   $199.00   $199.00  
  Purchase #6 $88.64   6.347%   $94.266   $94.27   $94.25   $94.30  
  Purchase #7 $244.29   9.853%   $268.3599   $268.36   $268.35   $268.40  
  7 purchase totals = $973.01       $1,074.7465   $1,074.76   $1,074.75   $1,074.80