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 $64.41   13.419%   $73.0532   $73.05   $73.05   $73.10  
  Purchase #2 $90.87   11.604%   $101.4146   $101.41   $101.40   $101.40  
  Purchase #3 $48.31   6.130%   $51.2714   $51.27   $51.25   $51.30  
  Purchase #4 $212.54   12.389%   $238.8716   $238.87   $238.85   $238.90  
  Purchase #5 $174.37   10.860%   $193.3066   $193.31   $193.30   $193.30  
  Purchase #6 $123.99   13.748%   $141.0361   $141.04   $141.05   $141.00  
  Purchase #7 $241.44   5.472%   $254.6516   $254.65   $254.65   $254.70  
  7 purchase totals = $955.93       $1,053.6051   $1,053.60   $1,053.55   $1,053.70