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 $86.67   8.283%   $93.8489   $93.85   $93.85   $93.80  
  Purchase #2 $35.99   8.577%   $39.0769   $39.08   $39.10   $39.10  
  Purchase #3 $60.93   7.253%   $65.3493   $65.35   $65.35   $65.30  
  Purchase #4 $206.33   7.774%   $222.3701   $222.37   $222.35   $222.40  
  Purchase #5 $53.97   5.227%   $56.791   $56.79   $56.80   $56.80  
  Purchase #6 $215.25   8.271%   $233.0533   $233.05   $233.05   $233.10  
  Purchase #7 $34.40   5.819%   $36.4017   $36.40   $36.40   $36.40  
  7 purchase totals = $693.54       $746.8912   $746.89   $746.90   $746.90