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 $31.36   13.307%   $35.5331   $35.53   $35.55   $35.50  
  Purchase #2 $213.26   6.284%   $226.6613   $226.66   $226.65   $226.70  
  Purchase #3 $77.60   4.730%   $81.2705   $81.27   $81.25   $81.30  
  Purchase #4 $88.40   11.842%   $98.8683   $98.87   $98.85   $98.90  
  Purchase #5 $96.74   13.323%   $109.6287   $109.63   $109.65   $109.60  
  Purchase #6 $12.51   7.785%   $13.4839   $13.48   $13.50   $13.50  
  Purchase #7 $133.80   11.410%   $149.0666   $149.07   $149.05   $149.10  
  7 purchase totals = $653.67       $714.5124   $714.51   $714.50   $714.60