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 $63.54   4.280%   $66.2595   $66.26   $66.25   $66.30  
  Purchase #2 $243.50   5.514%   $256.9266   $256.93   $256.95   $256.90  
  Purchase #3 $58.65   7.493%   $63.0446   $63.04   $63.05   $63.00  
  Purchase #4 $250.41   10.304%   $276.2122   $276.21   $276.20   $276.20  
  Purchase #5 $169.64   4.268%   $176.8802   $176.88   $176.90   $176.90  
  Purchase #6 $125.30   10.135%   $137.9992   $138.00   $138.00   $138.00  
  Purchase #7 $61.60   4.123%   $64.1398   $64.14   $64.15   $64.10  
  7 purchase totals = $972.64       $1,041.4621   $1,041.46   $1,041.50   $1,041.40