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 $61.92   11.861%   $69.2643   $69.26   $69.25   $69.30  
  Purchase #2 $242.76   7.713%   $261.4841   $261.48   $261.50   $261.50  
  Purchase #3 $124.52   5.211%   $131.0087   $131.01   $131.00   $131.00  
  Purchase #4 $47.80   4.258%   $49.8353   $49.84   $49.85   $49.80  
  Purchase #5 $215.86   9.438%   $236.2329   $236.23   $236.25   $236.20  
  Purchase #6 $113.82   6.736%   $121.4869   $121.49   $121.50   $121.50  
  Purchase #7 $71.77   12.553%   $80.7793   $80.78   $80.80   $80.80  
  7 purchase totals = $878.45       $950.0915   $950.09   $950.15   $950.10