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 $119.75   4.326%   $124.9304   $124.93   $124.95   $124.90  
  Purchase #2 $250.33   9.536%   $274.2015   $274.20   $274.20   $274.20  
  Purchase #3 $147.81   5.147%   $155.4178   $155.42   $155.40   $155.40  
  Purchase #4 $65.81   10.369%   $72.6338   $72.63   $72.65   $72.60  
  Purchase #5 $169.77   6.789%   $181.2957   $181.30   $181.30   $181.30  
  Purchase #6 $168.42   13.383%   $190.9596   $190.96   $190.95   $191.00  
  Purchase #7 $167.49   9.467%   $183.3463   $183.35   $183.35   $183.30  
  7 purchase totals = $1,089.38       $1,182.7851   $1,182.79   $1,182.80   $1,182.70