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 $34.66   5.579%   $36.5937   $36.59   $36.60   $36.60  
  Purchase #2 $77.76   11.402%   $86.6262   $86.63   $86.65   $86.60  
  Purchase #3 $101.32   6.419%   $107.8237   $107.82   $107.80   $107.80  
  Purchase #4 $69.57   10.136%   $76.6216   $76.62   $76.60   $76.60  
  Purchase #5 $25.69   9.292%   $28.0771   $28.08   $28.10   $28.10  
  Purchase #6 $190.96   7.540%   $205.3584   $205.36   $205.35   $205.40  
  Purchase #7 $179.28   4.449%   $187.2562   $187.26   $187.25   $187.30  
  7 purchase totals = $679.24       $728.3569   $728.36   $728.35   $728.40