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 $32.56   5.804%   $34.4498   $34.45   $34.45   $34.40  
  Purchase #2 $109.41   8.763%   $118.9976   $119.00   $119.00   $119.00  
  Purchase #3 $162.30   5.852%   $171.7978   $171.80   $171.80   $171.80  
  Purchase #4 $34.82   6.557%   $37.1031   $37.10   $37.10   $37.10  
  Purchase #5 $164.61   10.553%   $181.9813   $181.98   $182.00   $182.00  
  Purchase #6 $185.85   9.414%   $203.3459   $203.35   $203.35   $203.30  
  Purchase #7 $94.68   9.437%   $103.615   $103.62   $103.60   $103.60  
  7 purchase totals = $784.23       $851.2905   $851.30   $851.30   $851.20