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 $34.62   5.853%   $36.6463   $36.65   $36.65   $36.60  
  Purchase #2 $121.57   12.402%   $136.6471   $136.65   $136.65   $136.60  
  Purchase #3 $62.60   4.210%   $65.2355   $65.24   $65.25   $65.20  
  Purchase #4 $217.90   8.836%   $237.1536   $237.15   $237.15   $237.20  
  Purchase #5 $28.86   6.420%   $30.7128   $30.71   $30.70   $30.70  
  Purchase #6 $39.79   4.665%   $41.6462   $41.65   $41.65   $41.60  
  Purchase #7 $161.84   12.120%   $181.455   $181.46   $181.45   $181.50  
  7 purchase totals = $667.18       $729.4965   $729.51   $729.50   $729.40