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 $102.63   5.464%   $108.2377   $108.24   $108.25   $108.20  
  Purchase #2 $211.84   13.727%   $240.9193   $240.92   $240.90   $240.90  
  Purchase #3 $149.82   7.389%   $160.8902   $160.89   $160.90   $160.90  
  Purchase #4 $56.38   7.506%   $60.6119   $60.61   $60.60   $60.60  
  Purchase #5 $195.78   3.334%   $202.3073   $202.31   $202.30   $202.30  
  Purchase #6 $226.88   8.572%   $246.3282   $246.33   $246.35   $246.30  
  Purchase #7 $225.91   6.789%   $241.247   $241.25   $241.25   $241.20  
  7 purchase totals = $1,169.24       $1,260.5416   $1,260.55   $1,260.55   $1,260.40