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 $21.88   5.503%   $23.0841   $23.08   $23.10   $23.10  
  Purchase #2 $156.67   4.157%   $163.1828   $163.18   $163.20   $163.20  
  Purchase #3 $52.33   7.217%   $56.1067   $56.11   $56.10   $56.10  
  Purchase #4 $95.34   3.515%   $98.6912   $98.69   $98.70   $98.70  
  Purchase #5 $60.60   10.526%   $66.9788   $66.98   $67.00   $67.00  
  Purchase #6 $205.62   5.440%   $216.8057   $216.81   $216.80   $216.80  
  Purchase #7 $129.70   8.777%   $141.0838   $141.08   $141.10   $141.10  
  7 purchase totals = $722.14       $765.9331   $765.93   $766.00   $766.00