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 $46.92   8.113%   $50.7266   $50.73   $50.75   $50.70  
  Purchase #2 $231.98   8.466%   $251.6194   $251.62   $251.60   $251.60  
  Purchase #3 $50.44   11.596%   $56.289   $56.29   $56.30   $56.30  
  Purchase #4 $54.27   7.788%   $58.4965   $58.50   $58.50   $58.50  
  Purchase #5 $12.68   12.519%   $14.2674   $14.27   $14.25   $14.30  
  Purchase #6 $183.80   6.636%   $195.997   $196.00   $196.00   $196.00  
  Purchase #7 $167.82   8.464%   $182.0243   $182.02   $182.00   $182.00  
  7 purchase totals = $747.91       $809.4202   $809.43   $809.40   $809.40