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 $54.28   13.385%   $61.5454   $61.55   $61.55   $61.50  
  Purchase #2 $74.63   11.449%   $83.1744   $83.17   $83.15   $83.20  
  Purchase #3 $107.32   4.370%   $112.0099   $112.01   $112.00   $112.00  
  Purchase #4 $151.53   10.394%   $167.28   $167.28   $167.30   $167.30  
  Purchase #5 $97.88   3.590%   $101.3939   $101.39   $101.40   $101.40  
  Purchase #6 $229.76   5.661%   $242.7667   $242.77   $242.75   $242.80  
  Purchase #7 $181.38   11.772%   $202.7321   $202.73   $202.75   $202.70  
  7 purchase totals = $896.78       $970.9024   $970.90   $970.90   $970.90