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 $113.76   9.190%   $124.2145   $124.21   $124.20   $124.20  
  Purchase #2 $249.58   10.344%   $275.3966   $275.40   $275.40   $275.40  
  Purchase #3 $22.54   6.352%   $23.9717   $23.97   $23.95   $24.00  
  Purchase #4 $42.41   12.338%   $47.6425   $47.64   $47.65   $47.60  
  Purchase #5 $222.57   3.800%   $231.0277   $231.03   $231.05   $231.00  
  Purchase #6 $92.97   12.577%   $104.6628   $104.66   $104.65   $104.70  
  Purchase #7 $167.77   6.437%   $178.5694   $178.57   $178.55   $178.60  
  7 purchase totals = $911.60       $985.4852   $985.48   $985.45   $985.50