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 $100.83   8.564%   $109.4651   $109.47   $109.45   $109.50  
  Purchase #2 $75.72   12.836%   $85.4394   $85.44   $85.45   $85.40  
  Purchase #3 $77.46   13.177%   $87.6669   $87.67   $87.65   $87.70  
  Purchase #4 $95.67   9.629%   $104.8821   $104.88   $104.90   $104.90  
  Purchase #5 $26.98   7.133%   $28.9045   $28.90   $28.90   $28.90  
  Purchase #6 $22.34   12.472%   $25.1262   $25.13   $25.15   $25.10  
  Purchase #7 $199.32   8.302%   $215.8675   $215.87   $215.85   $215.90  
  7 purchase totals = $598.32       $657.3517   $657.36   $657.35   $657.40