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 $92.54   4.263%   $96.485   $96.49   $96.50   $96.50  
  Purchase #2 $234.97   3.337%   $242.8109   $242.81   $242.80   $242.80  
  Purchase #3 $133.87   7.203%   $143.5127   $143.51   $143.50   $143.50  
  Purchase #4 $106.71   8.346%   $115.616   $115.62   $115.60   $115.60  
  Purchase #5 $195.83   6.869%   $209.2816   $209.28   $209.30   $209.30  
  Purchase #6 $123.53   7.238%   $132.4711   $132.47   $132.45   $132.50  
  Purchase #7 $162.98   8.123%   $176.2189   $176.22   $176.20   $176.20  
  7 purchase totals = $1,050.43       $1,116.3962   $1,116.40   $1,116.35   $1,116.40