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 $231.91   5.627%   $244.9596   $244.96   $244.95   $245.00  
  Purchase #2 $155.98   13.194%   $176.56   $176.56   $176.55   $176.60  
  Purchase #3 $113.78   12.644%   $128.1663   $128.17   $128.15   $128.20  
  Purchase #4 $212.61   10.747%   $235.4592   $235.46   $235.45   $235.50  
  Purchase #5 $131.99   9.780%   $144.8986   $144.90   $144.90   $144.90  
  Purchase #6 $216.86   10.463%   $239.5501   $239.55   $239.55   $239.60  
  Purchase #7 $61.51   7.554%   $66.1565   $66.16   $66.15   $66.20  
  7 purchase totals = $1,124.64       $1,235.7503   $1,235.76   $1,235.70   $1,236.00