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 $95.92   8.779%   $104.3408   $104.34   $104.35   $104.30  
  Purchase #2 $53.32   11.118%   $59.2481   $59.25   $59.25   $59.20  
  Purchase #3 $30.35   12.742%   $34.2172   $34.22   $34.20   $34.20  
  Purchase #4 $184.67   13.521%   $209.6392   $209.64   $209.65   $209.60  
  Purchase #5 $32.68   13.743%   $37.1712   $37.17   $37.15   $37.20  
  Purchase #6 $240.67   11.635%   $268.672   $268.67   $268.65   $268.70  
  Purchase #7 $15.55   5.739%   $16.4424   $16.44   $16.45   $16.40  
  7 purchase totals = $653.16       $729.7309   $729.73   $729.70   $729.60