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 $247.39   8.463%   $268.3266   $268.33   $268.35   $268.30  
  Purchase #2 $96.36   10.682%   $106.6532   $106.65   $106.65   $106.70  
  Purchase #3 $125.79   13.401%   $142.6471   $142.65   $142.65   $142.60  
  Purchase #4 $232.94   9.824%   $255.824   $255.82   $255.80   $255.80  
  Purchase #5 $237.94   11.871%   $266.1859   $266.19   $266.20   $266.20  
  Purchase #6 $195.64   6.473%   $208.3038   $208.30   $208.30   $208.30  
  Purchase #7 $250.97   6.848%   $268.1564   $268.16   $268.15   $268.20  
  7 purchase totals = $1,387.03       $1,516.0970   $1,516.10   $1,516.10   $1,516.10