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 $42.44   13.190%   $48.0378   $48.04   $48.05   $48.00  
  Purchase #2 $129.29   11.733%   $144.4596   $144.46   $144.45   $144.50  
  Purchase #3 $247.35   6.125%   $262.5002   $262.50   $262.50   $262.50  
  Purchase #4 $62.33   7.235%   $66.8396   $66.84   $66.85   $66.80  
  Purchase #5 $241.50   3.682%   $250.392   $250.39   $250.40   $250.40  
  Purchase #6 $225.99   10.157%   $248.9438   $248.94   $248.95   $248.90  
  Purchase #7 $220.50   11.156%   $245.099   $245.10   $245.10   $245.10  
  7 purchase totals = $1,169.40       $1,266.2720   $1,266.27   $1,266.30   $1,266.20