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 $58.64   13.722%   $66.6866   $66.69   $66.70   $66.70  
  Purchase #2 $167.70   4.640%   $175.4813   $175.48   $175.50   $175.50  
  Purchase #3 $10.82   5.286%   $11.3919   $11.39   $11.40   $11.40  
  Purchase #4 $218.69   4.458%   $228.4392   $228.44   $228.45   $228.40  
  Purchase #5 $153.38   13.145%   $173.5418   $173.54   $173.55   $173.50  
  Purchase #6 $56.49   4.253%   $58.8925   $58.89   $58.90   $58.90  
  Purchase #7 $221.91   7.682%   $238.9571   $238.96   $238.95   $239.00  
  7 purchase totals = $887.63       $953.3904   $953.39   $953.45   $953.40