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 $69.62   9.274%   $76.0766   $76.08   $76.10   $76.10  
  Purchase #2 $96.33   11.742%   $107.6411   $107.64   $107.65   $107.60  
  Purchase #3 $26.54   9.441%   $29.0456   $29.05   $29.05   $29.00  
  Purchase #4 $63.49   8.818%   $69.0885   $69.09   $69.10   $69.10  
  Purchase #5 $208.86   11.426%   $232.7243   $232.72   $232.70   $232.70  
  Purchase #6 $190.95   8.723%   $207.6066   $207.61   $207.60   $207.60  
  Purchase #7 $96.70   3.226%   $99.8195   $99.82   $99.80   $99.80  
  7 purchase totals = $752.49       $822.0022   $822.01   $822.00   $821.90