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 $26.28   10.354%   $29.001   $29.00   $29.00   $29.00  
  Purchase #2 $16.43   5.116%   $17.2706   $17.27   $17.25   $17.30  
  Purchase #3 $16.71   4.258%   $17.4215   $17.42   $17.40   $17.40  
  Purchase #4 $160.62   8.787%   $174.7337   $174.73   $174.75   $174.70  
  Purchase #5 $201.27   8.427%   $218.231   $218.23   $218.25   $218.20  
  Purchase #6 $129.75   8.720%   $141.0642   $141.06   $141.05   $141.10  
  Purchase #7 $188.51   6.635%   $201.0176   $201.02   $201.00   $201.00  
  7 purchase totals = $739.57       $798.7396   $798.73   $798.70   $798.70