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 $188.97   8.411%   $204.8643   $204.86   $204.85   $204.90  
  Purchase #2 $211.84   4.183%   $220.7013   $220.70   $220.70   $220.70  
  Purchase #3 $193.82   11.811%   $216.7121   $216.71   $216.70   $216.70  
  Purchase #4 $51.73   10.554%   $57.1896   $57.19   $57.20   $57.20  
  Purchase #5 $109.76   11.206%   $122.0597   $122.06   $122.05   $122.10  
  Purchase #6 $34.41   3.573%   $35.6395   $35.64   $35.65   $35.60  
  Purchase #7 $197.29   8.871%   $214.7916   $214.79   $214.80   $214.80  
  7 purchase totals = $987.82       $1,071.9581   $1,071.95   $1,071.95   $1,072.00