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 $55.85   8.160%   $60.4074   $60.41   $60.40   $60.40  
  Purchase #2 $192.94   11.401%   $214.9371   $214.94   $214.95   $214.90  
  Purchase #3 $218.26   9.194%   $238.3268   $238.33   $238.35   $238.30  
  Purchase #4 $82.69   5.832%   $87.5125   $87.51   $87.50   $87.50  
  Purchase #5 $6.97   11.733%   $7.7878   $7.79   $7.80   $7.80  
  Purchase #6 $212.30   10.401%   $234.3813   $234.38   $234.40   $234.40  
  Purchase #7 $186.74   12.853%   $210.7417   $210.74   $210.75   $210.70  
  7 purchase totals = $955.75       $1,054.0946   $1,054.10   $1,054.15   $1,054.00