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 $67.99   12.808%   $76.6982   $76.70   $76.70   $76.70  
  Purchase #2 $118.53   10.822%   $131.3573   $131.36   $131.35   $131.40  
  Purchase #3 $217.61   10.117%   $239.6256   $239.63   $239.65   $239.60  
  Purchase #4 $62.79   12.748%   $70.7945   $70.79   $70.80   $70.80  
  Purchase #5 $36.47   3.313%   $37.6783   $37.68   $37.70   $37.70  
  Purchase #6 $130.32   10.733%   $144.3072   $144.31   $144.30   $144.30  
  Purchase #7 $233.57   5.869%   $247.2782   $247.28   $247.30   $247.30  
  7 purchase totals = $867.28       $947.7393   $947.75   $947.80   $947.80