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 $132.91   6.216%   $141.1717   $141.17   $141.15   $141.20  
  Purchase #2 $64.89   6.818%   $69.3142   $69.31   $69.30   $69.30  
  Purchase #3 $112.35   4.394%   $117.2867   $117.29   $117.30   $117.30  
  Purchase #4 $211.80   7.102%   $226.842   $226.84   $226.85   $226.80  
  Purchase #5 $58.28   8.789%   $63.4022   $63.40   $63.40   $63.40  
  Purchase #6 $232.91   12.376%   $261.7349   $261.73   $261.75   $261.70  
  Purchase #7 $190.64   12.306%   $214.1002   $214.10   $214.10   $214.10  
  7 purchase totals = $1,003.78       $1,093.8519   $1,093.84   $1,093.85   $1,093.80