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 $192.77   13.226%   $218.2658   $218.27   $218.25   $218.30  
  Purchase #2 $168.57   11.323%   $187.6572   $187.66   $187.65   $187.70  
  Purchase #3 $9.51   6.491%   $10.1273   $10.13   $10.15   $10.10  
  Purchase #4 $22.66   11.746%   $25.3216   $25.32   $25.30   $25.30  
  Purchase #5 $180.66   9.837%   $198.4315   $198.43   $198.45   $198.40  
  Purchase #6 $109.69   3.674%   $113.72   $113.72   $113.70   $113.70  
  Purchase #7 $48.33   5.436%   $50.9572   $50.96   $50.95   $51.00  
  7 purchase totals = $732.19       $804.4806   $804.49   $804.45   $804.50