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 $69.71   10.849%   $77.2728   $77.27   $77.25   $77.30  
  Purchase #2 $189.97   10.771%   $210.4317   $210.43   $210.45   $210.40  
  Purchase #3 $214.67   4.530%   $224.3946   $224.39   $224.40   $224.40  
  Purchase #4 $237.98   6.518%   $253.4915   $253.49   $253.50   $253.50  
  Purchase #5 $31.83   11.667%   $35.5436   $35.54   $35.55   $35.50  
  Purchase #6 $18.42   7.670%   $19.8328   $19.83   $19.85   $19.80  
  Purchase #7 $204.70   5.680%   $216.327   $216.33   $216.35   $216.30  
  7 purchase totals = $967.28       $1,037.2940   $1,037.28   $1,037.35   $1,037.20