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 $68.72   6.673%   $73.3057   $73.31   $73.30   $73.30  
  Purchase #2 $191.77   9.591%   $210.1627   $210.16   $210.15   $210.20  
  Purchase #3 $183.49   8.374%   $198.8555   $198.86   $198.85   $198.90  
  Purchase #4 $147.85   13.193%   $167.3559   $167.36   $167.35   $167.40  
  Purchase #5 $64.38   6.229%   $68.3902   $68.39   $68.40   $68.40  
  Purchase #6 $98.96   3.321%   $102.2465   $102.25   $102.25   $102.20  
  Purchase #7 $37.38   5.636%   $39.4867   $39.49   $39.50   $39.50  
  7 purchase totals = $792.55       $859.8032   $859.82   $859.80   $859.90