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 $241.72   11.302%   $269.0392   $269.04   $269.05   $269.00  
  Purchase #2 $150.52   8.138%   $162.7693   $162.77   $162.75   $162.80  
  Purchase #3 $69.29   4.521%   $72.4226   $72.42   $72.40   $72.40  
  Purchase #4 $26.70   12.175%   $29.9507   $29.95   $29.95   $30.00  
  Purchase #5 $225.35   7.380%   $241.9808   $241.98   $242.00   $242.00  
  Purchase #6 $171.69   11.487%   $191.412   $191.41   $191.40   $191.40  
  Purchase #7 $200.44   5.138%   $210.7386   $210.74   $210.75   $210.70  
  7 purchase totals = $1,085.71       $1,178.3132   $1,178.31   $1,178.30   $1,178.30