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 $169.97   9.784%   $186.5999   $186.60   $186.60   $186.60  
  Purchase #2 $187.47   9.197%   $204.7116   $204.71   $204.70   $204.70  
  Purchase #3 $232.66   11.473%   $259.3531   $259.35   $259.35   $259.40  
  Purchase #4 $224.35   8.193%   $242.731   $242.73   $242.75   $242.70  
  Purchase #5 $196.83   4.529%   $205.7444   $205.74   $205.75   $205.70  
  Purchase #6 $115.78   9.428%   $126.6957   $126.70   $126.70   $126.70  
  Purchase #7 $208.93   11.518%   $232.9946   $232.99   $233.00   $233.00  
  7 purchase totals = $1,335.99       $1,458.8303   $1,458.82   $1,458.85   $1,458.80