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 $87.47   9.618%   $95.8829   $95.88   $95.90   $95.90  
  Purchase #2 $209.69   12.411%   $235.7146   $235.71   $235.70   $235.70  
  Purchase #3 $27.56   6.332%   $29.3051   $29.31   $29.30   $29.30  
  Purchase #4 $192.53   4.806%   $201.783   $201.78   $201.80   $201.80  
  Purchase #5 $69.87   12.548%   $78.6373   $78.64   $78.65   $78.60  
  Purchase #6 $111.27   6.735%   $118.764   $118.76   $118.75   $118.80  
  Purchase #7 $60.58   10.838%   $67.1457   $67.15   $67.15   $67.10  
  7 purchase totals = $758.97       $827.2326   $827.23   $827.25   $827.20