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 $171.89   13.626%   $195.3117   $195.31   $195.30   $195.30  
  Purchase #2 $218.46   4.648%   $228.614   $228.61   $228.60   $228.60  
  Purchase #3 $74.69   4.516%   $78.063   $78.06   $78.05   $78.10  
  Purchase #4 $156.97   6.547%   $167.2468   $167.25   $167.25   $167.20  
  Purchase #5 $233.90   7.861%   $252.2869   $252.29   $252.30   $252.30  
  Purchase #6 $179.67   3.127%   $185.2883   $185.29   $185.30   $185.30  
  Purchase #7 $228.44   3.769%   $237.0499   $237.05   $237.05   $237.00  
  7 purchase totals = $1,264.02       $1,343.8606   $1,343.86   $1,343.85   $1,343.80