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 $46.66   4.152%   $48.5973   $48.60   $48.60   $48.60  
  Purchase #2 $72.81   9.293%   $79.5762   $79.58   $79.60   $79.60  
  Purchase #3 $235.74   4.633%   $246.6618   $246.66   $246.65   $246.70  
  Purchase #4 $219.99   11.547%   $245.3922   $245.39   $245.40   $245.40  
  Purchase #5 $146.43   7.859%   $157.9379   $157.94   $157.95   $157.90  
  Purchase #6 $141.62   12.321%   $159.069   $159.07   $159.05   $159.10  
  Purchase #7 $152.57   4.502%   $159.4387   $159.44   $159.45   $159.40  
  7 purchase totals = $1,015.82       $1,096.6731   $1,096.68   $1,096.70   $1,096.70