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 $46.97   7.298%   $50.3979   $50.40   $50.40   $50.40  
  Purchase #2 $218.71   11.855%   $244.6381   $244.64   $244.65   $244.60  
  Purchase #3 $64.31   10.549%   $71.0941   $71.09   $71.10   $71.10  
  Purchase #4 $236.32   13.567%   $268.3815   $268.38   $268.40   $268.40  
  Purchase #5 $205.79   3.647%   $213.2952   $213.30   $213.30   $213.30  
  Purchase #6 $226.32   8.445%   $245.4327   $245.43   $245.45   $245.40  
  Purchase #7 $175.51   4.467%   $183.35   $183.35   $183.35   $183.40  
  7 purchase totals = $1,173.93       $1,276.5895   $1,276.59   $1,276.65   $1,276.60