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 $84.62   11.771%   $94.5806   $94.58   $94.60   $94.60  
  Purchase #2 $181.28   3.681%   $187.9529   $187.95   $187.95   $188.00  
  Purchase #3 $22.47   8.864%   $24.4617   $24.46   $24.45   $24.50  
  Purchase #4 $95.42   4.870%   $100.067   $100.07   $100.05   $100.10  
  Purchase #5 $13.50   7.720%   $14.5422   $14.54   $14.55   $14.50  
  Purchase #6 $141.71   8.400%   $153.6136   $153.61   $153.60   $153.60  
  Purchase #7 $229.79   7.451%   $246.9117   $246.91   $246.90   $246.90  
  7 purchase totals = $768.79       $822.1297   $822.12   $822.10   $822.20