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 $56.64   9.446%   $61.9902   $61.99   $62.00   $62.00  
  Purchase #2 $238.92   13.561%   $271.3199   $271.32   $271.30   $271.30  
  Purchase #3 $73.38   8.643%   $79.7222   $79.72   $79.70   $79.70  
  Purchase #4 $207.61   4.287%   $216.5102   $216.51   $216.50   $216.50  
  Purchase #5 $63.55   5.629%   $67.1272   $67.13   $67.15   $67.10  
  Purchase #6 $160.71   9.492%   $175.9646   $175.96   $175.95   $176.00  
  Purchase #7 $249.46   12.185%   $279.8567   $279.86   $279.85   $279.90  
  7 purchase totals = $1,050.27       $1,152.4910   $1,152.49   $1,152.45   $1,152.50