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 $250.44   13.627%   $284.5675   $284.57   $284.55   $284.60  
  Purchase #2 $170.67   7.500%   $183.4703   $183.47   $183.45   $183.50  
  Purchase #3 $124.60   7.809%   $134.33   $134.33   $134.35   $134.30  
  Purchase #4 $142.56   11.778%   $159.3507   $159.35   $159.35   $159.40  
  Purchase #5 $185.38   5.489%   $195.5555   $195.56   $195.55   $195.60  
  Purchase #6 $209.80   7.148%   $224.7965   $224.80   $224.80   $224.80  
  Purchase #7 $22.95   7.581%   $24.6898   $24.69   $24.70   $24.70  
  7 purchase totals = $1,106.40       $1,206.7603   $1,206.77   $1,206.75   $1,206.90