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 $217.51   13.867%   $247.6721   $247.67   $247.65   $247.70  
  Purchase #2 $227.64   5.674%   $240.5563   $240.56   $240.55   $240.60  
  Purchase #3 $89.99   8.472%   $97.614   $97.61   $97.60   $97.60  
  Purchase #4 $212.41   8.494%   $230.4521   $230.45   $230.45   $230.50  
  Purchase #5 $214.26   12.304%   $240.6226   $240.62   $240.60   $240.60  
  Purchase #6 $237.55   5.498%   $250.6105   $250.61   $250.60   $250.60  
  Purchase #7 $207.69   9.619%   $227.6677   $227.67   $227.65   $227.70  
  7 purchase totals = $1,407.05       $1,535.1953   $1,535.19   $1,535.10   $1,535.30