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 $216.28   10.253%   $238.4552   $238.46   $238.45   $238.50  
  Purchase #2 $198.36   10.251%   $218.6939   $218.69   $218.70   $218.70  
  Purchase #3 $87.41   9.433%   $95.6554   $95.66   $95.65   $95.70  
  Purchase #4 $49.65   5.202%   $52.2328   $52.23   $52.25   $52.20  
  Purchase #5 $59.66   11.625%   $66.5955   $66.60   $66.60   $66.60  
  Purchase #6 $46.36   7.227%   $49.7104   $49.71   $49.70   $49.70  
  Purchase #7 $218.58   10.779%   $242.1407   $242.14   $242.15   $242.10  
  7 purchase totals = $876.30       $963.4839   $963.49   $963.50   $963.50