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 $214.42   12.708%   $241.6685   $241.67   $241.65   $241.70  
  Purchase #2 $113.69   11.569%   $126.8428   $126.84   $126.85   $126.80  
  Purchase #3 $233.27   10.811%   $258.4888   $258.49   $258.50   $258.50  
  Purchase #4 $84.40   3.507%   $87.3599   $87.36   $87.35   $87.40  
  Purchase #5 $187.93   4.772%   $196.898   $196.90   $196.90   $196.90  
  Purchase #6 $138.97   10.600%   $153.7008   $153.70   $153.70   $153.70  
  Purchase #7 $197.66   5.185%   $207.9087   $207.91   $207.90   $207.90  
  7 purchase totals = $1,170.34       $1,272.8675   $1,272.87   $1,272.85   $1,272.90