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 $119.60   12.563%   $134.6253   $134.63   $134.65   $134.60  
  Purchase #2 $229.60   9.184%   $250.6865   $250.69   $250.70   $250.70  
  Purchase #3 $98.52   9.321%   $107.703   $107.70   $107.70   $107.70  
  Purchase #4 $179.97   7.846%   $194.0904   $194.09   $194.10   $194.10  
  Purchase #5 $15.27   9.593%   $16.7349   $16.73   $16.75   $16.70  
  Purchase #6 $239.35   3.224%   $247.0666   $247.07   $247.05   $247.10  
  Purchase #7 $14.90   12.844%   $16.8138   $16.81   $16.80   $16.80  
  7 purchase totals = $897.21       $967.7205   $967.72   $967.75   $967.70