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 $228.29   8.319%   $247.2814   $247.28   $247.30   $247.30  
  Purchase #2 $54.80   5.711%   $57.9296   $57.93   $57.95   $57.90  
  Purchase #3 $248.84   11.547%   $277.5736   $277.57   $277.55   $277.60  
  Purchase #4 $199.45   7.416%   $214.2412   $214.24   $214.25   $214.20  
  Purchase #5 $227.46   6.711%   $242.7248   $242.72   $242.70   $242.70  
  Purchase #6 $49.44   12.162%   $55.4529   $55.45   $55.45   $55.50  
  Purchase #7 $237.78   10.675%   $263.163   $263.16   $263.15   $263.20  
  7 purchase totals = $1,246.06       $1,358.3665   $1,358.35   $1,358.35   $1,358.40