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 $234.62   11.855%   $262.4342   $262.43   $262.45   $262.40  
  Purchase #2 $56.44   11.141%   $62.728   $62.73   $62.75   $62.70  
  Purchase #3 $201.97   5.418%   $212.9127   $212.91   $212.90   $212.90  
  Purchase #4 $113.31   5.529%   $119.5749   $119.57   $119.55   $119.60  
  Purchase #5 $135.58   4.712%   $141.9685   $141.97   $141.95   $142.00  
  Purchase #6 $218.53   12.782%   $246.4625   $246.46   $246.45   $246.50  
  Purchase #7 $164.50   3.338%   $169.991   $169.99   $170.00   $170.00  
  7 purchase totals = $1,124.95       $1,216.0718   $1,216.06   $1,216.05   $1,216.10