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 $86.95   6.217%   $92.3557   $92.36   $92.35   $92.40  
  Purchase #2 $80.46   4.691%   $84.2344   $84.23   $84.25   $84.20  
  Purchase #3 $182.47   11.302%   $203.0928   $203.09   $203.10   $203.10  
  Purchase #4 $225.74   8.829%   $245.6706   $245.67   $245.65   $245.70  
  Purchase #5 $93.71   6.513%   $99.8133   $99.81   $99.80   $99.80  
  Purchase #6 $240.82   11.451%   $268.3963   $268.40   $268.40   $268.40  
  Purchase #7 $213.93   5.794%   $226.3251   $226.33   $226.35   $226.30  
  7 purchase totals = $1,124.08       $1,219.8882   $1,219.89   $1,219.90   $1,219.90