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 $147.38   6.475%   $156.9229   $156.92   $156.90   $156.90  
  Purchase #2 $54.70   5.632%   $57.7807   $57.78   $57.80   $57.80  
  Purchase #3 $165.75   4.387%   $173.0215   $173.02   $173.00   $173.00  
  Purchase #4 $92.89   3.269%   $95.9266   $95.93   $95.95   $95.90  
  Purchase #5 $234.34   4.797%   $245.5813   $245.58   $245.60   $245.60  
  Purchase #6 $245.27   6.200%   $260.4767   $260.48   $260.50   $260.50  
  Purchase #7 $65.48   6.777%   $69.9176   $69.92   $69.90   $69.90  
  7 purchase totals = $1,005.81       $1,059.6273   $1,059.63   $1,059.65   $1,059.60