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 $241.69   9.682%   $265.0904   $265.09   $265.10   $265.10  
  Purchase #2 $149.99   6.635%   $159.9418   $159.94   $159.95   $159.90  
  Purchase #3 $128.57   3.147%   $132.6161   $132.62   $132.60   $132.60  
  Purchase #4 $59.51   6.871%   $63.5989   $63.60   $63.60   $63.60  
  Purchase #5 $231.74   6.813%   $247.5284   $247.53   $247.55   $247.50  
  Purchase #6 $96.99   3.195%   $100.0888   $100.09   $100.10   $100.10  
  Purchase #7 $72.82   6.256%   $77.3756   $77.38   $77.40   $77.40  
  7 purchase totals = $981.31       $1,046.2400   $1,046.25   $1,046.30   $1,046.20