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 $193.87   12.758%   $218.6039   $218.60   $218.60   $218.60  
  Purchase #2 $86.43   5.392%   $91.0903   $91.09   $91.10   $91.10  
  Purchase #3 $242.51   7.198%   $259.9659   $259.97   $259.95   $260.00  
  Purchase #4 $169.29   3.488%   $175.1948   $175.19   $175.20   $175.20  
  Purchase #5 $158.30   3.796%   $164.3091   $164.31   $164.30   $164.30  
  Purchase #6 $212.44   8.618%   $230.7481   $230.75   $230.75   $230.70  
  Purchase #7 $58.70   12.423%   $65.9923   $65.99   $66.00   $66.00  
  7 purchase totals = $1,121.54       $1,205.9044   $1,205.90   $1,205.90   $1,205.90