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 $191.35   5.874%   $202.5899   $202.59   $202.60   $202.60  
  Purchase #2 $18.27   10.235%   $20.1399   $20.14   $20.15   $20.10  
  Purchase #3 $77.78   10.384%   $85.8567   $85.86   $85.85   $85.90  
  Purchase #4 $95.25   13.612%   $108.2154   $108.22   $108.20   $108.20  
  Purchase #5 $200.93   5.855%   $212.6945   $212.69   $212.70   $212.70  
  Purchase #6 $37.32   9.669%   $40.9285   $40.93   $40.95   $40.90  
  Purchase #7 $85.69   10.426%   $94.624   $94.62   $94.60   $94.60  
  7 purchase totals = $706.59       $765.0489   $765.05   $765.05   $765.00