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 $85.29   10.529%   $94.2702   $94.27   $94.25   $94.30  
  Purchase #2 $92.80   7.856%   $100.0904   $100.09   $100.10   $100.10  
  Purchase #3 $13.87   8.158%   $15.0015   $15.00   $15.00   $15.00  
  Purchase #4 $223.76   4.208%   $233.1758   $233.18   $233.20   $233.20  
  Purchase #5 $246.81   8.262%   $267.2014   $267.20   $267.20   $267.20  
  Purchase #6 $90.33   6.561%   $96.2566   $96.26   $96.25   $96.30  
  Purchase #7 $65.88   8.164%   $71.2584   $71.26   $71.25   $71.30  
  7 purchase totals = $818.74       $877.2543   $877.26   $877.25   $877.40