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 $89.89   4.103%   $93.5782   $93.58   $93.60   $93.60  
  Purchase #2 $51.65   9.484%   $56.5485   $56.55   $56.55   $56.50  
  Purchase #3 $35.54   3.240%   $36.6915   $36.69   $36.70   $36.70  
  Purchase #4 $102.31   12.686%   $115.289   $115.29   $115.30   $115.30  
  Purchase #5 $30.34   12.112%   $34.0148   $34.01   $34.00   $34.00  
  Purchase #6 $233.38   4.212%   $243.21   $243.21   $243.20   $243.20  
  Purchase #7 $87.77   10.595%   $97.0692   $97.07   $97.05   $97.10  
  7 purchase totals = $630.88       $676.4012   $676.40   $676.40   $676.40