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 $57.84   6.662%   $61.6933   $61.69   $61.70   $61.70  
  Purchase #2 $6.61   9.604%   $7.2448   $7.24   $7.25   $7.20  
  Purchase #3 $181.47   7.478%   $195.0403   $195.04   $195.05   $195.00  
  Purchase #4 $130.53   7.753%   $140.65   $140.65   $140.65   $140.70  
  Purchase #5 $128.55   8.729%   $139.7711   $139.77   $139.75   $139.80  
  Purchase #6 $187.77   11.765%   $209.8611   $209.86   $209.85   $209.90  
  Purchase #7 $164.30   8.411%   $178.1193   $178.12   $178.10   $178.10  
  7 purchase totals = $857.07       $932.3799   $932.37   $932.35   $932.40