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 $51.67   4.564%   $54.0282   $54.03   $54.05   $54.00  
  Purchase #2 $228.84   7.806%   $246.7033   $246.70   $246.70   $246.70  
  Purchase #3 $72.86   8.170%   $78.8127   $78.81   $78.80   $78.80  
  Purchase #4 $151.79   5.853%   $160.6743   $160.67   $160.65   $160.70  
  Purchase #5 $19.33   8.158%   $20.9069   $20.91   $20.90   $20.90  
  Purchase #6 $103.41   13.188%   $117.0477   $117.05   $117.05   $117.00  
  Purchase #7 $239.75   13.660%   $272.4999   $272.50   $272.50   $272.50  
  7 purchase totals = $867.65       $950.6730   $950.67   $950.65   $950.60