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 $162.68   8.611%   $176.6884   $176.69   $176.70   $176.70  
  Purchase #2 $228.68   12.249%   $256.691   $256.69   $256.70   $256.70  
  Purchase #3 $246.68   11.111%   $274.0886   $274.09   $274.10   $274.10  
  Purchase #4 $196.89   4.295%   $205.3464   $205.35   $205.35   $205.30  
  Purchase #5 $107.56   3.659%   $111.4956   $111.50   $111.50   $111.50  
  Purchase #6 $229.38   13.276%   $259.8325   $259.83   $259.85   $259.80  
  Purchase #7 $194.34   12.206%   $218.0611   $218.06   $218.05   $218.10  
  7 purchase totals = $1,366.21       $1,502.2036   $1,502.21   $1,502.25   $1,502.20