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 $235.40   12.191%   $264.0976   $264.10   $264.10   $264.10  
  Purchase #2 $104.87   7.841%   $113.0929   $113.09   $113.10   $113.10  
  Purchase #3 $76.66   7.634%   $82.5122   $82.51   $82.50   $82.50  
  Purchase #4 $226.42   9.470%   $247.862   $247.86   $247.85   $247.90  
  Purchase #5 $250.79   3.800%   $260.32   $260.32   $260.30   $260.30  
  Purchase #6 $55.80   12.105%   $62.5546   $62.55   $62.55   $62.60  
  Purchase #7 $21.48   7.782%   $23.1516   $23.15   $23.15   $23.20  
  7 purchase totals = $971.42       $1,053.5909   $1,053.58   $1,053.55   $1,053.70