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 $112.51   12.469%   $126.5389   $126.54   $126.55   $126.50  
  Purchase #2 $153.91   7.223%   $165.0269   $165.03   $165.05   $165.00  
  Purchase #3 $137.30   3.539%   $142.159   $142.16   $142.15   $142.20  
  Purchase #4 $98.30   7.414%   $105.588   $105.59   $105.60   $105.60  
  Purchase #5 $80.48   3.557%   $83.3427   $83.34   $83.35   $83.30  
  Purchase #6 $181.67   7.448%   $195.2008   $195.20   $195.20   $195.20  
  Purchase #7 $65.81   12.838%   $74.2587   $74.26   $74.25   $74.30  
  7 purchase totals = $829.98       $892.1150   $892.12   $892.15   $892.10