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 $69.71   7.873%   $75.1983   $75.20   $75.20   $75.20  
  Purchase #2 $64.44   5.521%   $67.9977   $68.00   $68.00   $68.00  
  Purchase #3 $62.83   9.755%   $68.9591   $68.96   $68.95   $69.00  
  Purchase #4 $225.99   6.731%   $241.2014   $241.20   $241.20   $241.20  
  Purchase #5 $169.36   8.230%   $183.2983   $183.30   $183.30   $183.30  
  Purchase #6 $29.25   3.667%   $30.3226   $30.32   $30.30   $30.30  
  Purchase #7 $74.95   13.338%   $84.9468   $84.95   $84.95   $84.90  
  7 purchase totals = $696.53       $751.9242   $751.93   $751.90   $751.90