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 $203.74   10.214%   $224.55   $224.55   $224.55   $224.60  
  Purchase #2 $84.38   13.686%   $95.9282   $95.93   $95.95   $95.90  
  Purchase #3 $162.74   11.296%   $181.1231   $181.12   $181.10   $181.10  
  Purchase #4 $76.50   4.322%   $79.8063   $79.81   $79.80   $79.80  
  Purchase #5 $71.66   7.149%   $76.783   $76.78   $76.80   $76.80  
  Purchase #6 $48.44   4.723%   $50.7278   $50.73   $50.75   $50.70  
  Purchase #7 $60.78   7.544%   $65.3652   $65.37   $65.35   $65.40  
  7 purchase totals = $708.24       $774.2836   $774.29   $774.30   $774.30