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 $246.84   8.387%   $267.5425   $267.54   $267.55   $267.50  
  Purchase #2 $92.98   3.214%   $95.9684   $95.97   $95.95   $96.00  
  Purchase #3 $77.36   8.637%   $84.0416   $84.04   $84.05   $84.00  
  Purchase #4 $211.49   13.831%   $240.7412   $240.74   $240.75   $240.70  
  Purchase #5 $100.85   8.235%   $109.155   $109.16   $109.15   $109.20  
  Purchase #6 $193.81   10.447%   $214.0573   $214.06   $214.05   $214.10  
  Purchase #7 $100.87   12.391%   $113.3688   $113.37   $113.35   $113.40  
  7 purchase totals = $1,024.20       $1,124.8748   $1,124.88   $1,124.85   $1,124.90