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 $241.62   10.577%   $267.1761   $267.18   $267.20   $267.20  
  Purchase #2 $144.41   9.173%   $157.6567   $157.66   $157.65   $157.70  
  Purchase #3 $35.99   7.811%   $38.8012   $38.80   $38.80   $38.80  
  Purchase #4 $86.89   5.298%   $91.4934   $91.49   $91.50   $91.50  
  Purchase #5 $44.73   11.621%   $49.9281   $49.93   $49.95   $49.90  
  Purchase #6 $150.63   11.407%   $167.8124   $167.81   $167.80   $167.80  
  Purchase #7 $80.83   6.357%   $85.9684   $85.97   $85.95   $86.00  
  7 purchase totals = $785.10       $858.8363   $858.84   $858.85   $858.90