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 $218.67   11.722%   $244.3025   $244.30   $244.30   $244.30  
  Purchase #2 $142.88   6.155%   $151.6743   $151.67   $151.65   $151.70  
  Purchase #3 $152.91   9.377%   $167.2484   $167.25   $167.25   $167.20  
  Purchase #4 $235.96   4.545%   $246.6844   $246.68   $246.70   $246.70  
  Purchase #5 $198.29   8.132%   $214.4149   $214.41   $214.40   $214.40  
  Purchase #6 $78.37   3.423%   $81.0526   $81.05   $81.05   $81.10  
  Purchase #7 $248.37   9.824%   $272.7699   $272.77   $272.75   $272.80  
  7 purchase totals = $1,275.45       $1,378.1470   $1,378.13   $1,378.10   $1,378.20