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 $249.54   5.179%   $262.4637   $262.46   $262.45   $262.50  
  Purchase #2 $143.50   6.866%   $153.3527   $153.35   $153.35   $153.40  
  Purchase #3 $181.75   6.874%   $194.2435   $194.24   $194.25   $194.20  
  Purchase #4 $122.66   13.130%   $138.7653   $138.77   $138.75   $138.80  
  Purchase #5 $110.25   5.457%   $116.2663   $116.27   $116.25   $116.30  
  Purchase #6 $30.25   11.430%   $33.7076   $33.71   $33.70   $33.70  
  Purchase #7 $222.28   6.503%   $236.7349   $236.73   $236.75   $236.70  
  7 purchase totals = $1,060.23       $1,135.5340   $1,135.53   $1,135.50   $1,135.60