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 $48.71   6.665%   $51.9565   $51.96   $51.95   $52.00  
  Purchase #2 $156.86   9.108%   $171.1468   $171.15   $171.15   $171.10  
  Purchase #3 $113.71   8.765%   $123.6767   $123.68   $123.70   $123.70  
  Purchase #4 $151.47   8.523%   $164.3798   $164.38   $164.40   $164.40  
  Purchase #5 $64.56   7.859%   $69.6338   $69.63   $69.65   $69.60  
  Purchase #6 $164.68   13.180%   $186.3848   $186.38   $186.40   $186.40  
  Purchase #7 $205.63   5.463%   $216.8636   $216.86   $216.85   $216.90  
  7 purchase totals = $905.62       $984.0420   $984.04   $984.10   $984.10