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 $193.64   12.559%   $217.9592   $217.96   $217.95   $218.00  
  Purchase #2 $201.36   10.623%   $222.7505   $222.75   $222.75   $222.80  
  Purchase #3 $171.92   4.852%   $180.2616   $180.26   $180.25   $180.30  
  Purchase #4 $22.38   9.245%   $24.449   $24.45   $24.45   $24.40  
  Purchase #5 $54.99   8.169%   $59.4821   $59.48   $59.50   $59.50  
  Purchase #6 $194.81   9.115%   $212.5669   $212.57   $212.55   $212.60  
  Purchase #7 $112.65   5.662%   $119.0282   $119.03   $119.05   $119.00  
  7 purchase totals = $951.75       $1,036.4975   $1,036.50   $1,036.50   $1,036.60