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 $111.56   11.859%   $124.7899   $124.79   $124.80   $124.80  
  Purchase #2 $218.49   10.148%   $240.6624   $240.66   $240.65   $240.70  
  Purchase #3 $139.68   11.223%   $155.3563   $155.36   $155.35   $155.40  
  Purchase #4 $199.97   3.406%   $206.781   $206.78   $206.80   $206.80  
  Purchase #5 $130.60   10.445%   $144.2412   $144.24   $144.25   $144.20  
  Purchase #6 $153.54   7.797%   $165.5115   $165.51   $165.50   $165.50  
  Purchase #7 $15.48   3.785%   $16.0659   $16.07   $16.05   $16.10  
  7 purchase totals = $969.32       $1,053.4082   $1,053.41   $1,053.40   $1,053.50