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 $152.64   13.553%   $173.3273   $173.33   $173.35   $173.30  
  Purchase #2 $127.38   8.351%   $138.0175   $138.02   $138.00   $138.00  
  Purchase #3 $41.38   12.598%   $46.5931   $46.59   $46.60   $46.60  
  Purchase #4 $59.99   13.153%   $67.8805   $67.88   $67.90   $67.90  
  Purchase #5 $24.96   4.324%   $26.0393   $26.04   $26.05   $26.00  
  Purchase #6 $180.92   6.152%   $192.0502   $192.05   $192.05   $192.10  
  Purchase #7 $164.46   10.181%   $181.2037   $181.20   $181.20   $181.20  
  7 purchase totals = $751.73       $825.1116   $825.11   $825.15   $825.10