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 $64.82   5.253%   $68.225   $68.23   $68.25   $68.20  
  Purchase #2 $26.34   5.330%   $27.7439   $27.74   $27.75   $27.70  
  Purchase #3 $21.60   9.366%   $23.6231   $23.62   $23.60   $23.60  
  Purchase #4 $235.89   12.370%   $265.0696   $265.07   $265.05   $265.10  
  Purchase #5 $197.25   3.374%   $203.9052   $203.91   $203.90   $203.90  
  Purchase #6 $241.67   4.314%   $252.0956   $252.10   $252.10   $252.10  
  Purchase #7 $237.47   7.365%   $254.9597   $254.96   $254.95   $255.00  
  7 purchase totals = $1,025.04       $1,095.6221   $1,095.63   $1,095.60   $1,095.60