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 $55.87   10.504%   $61.7386   $61.74   $61.75   $61.70  
  Purchase #2 $227.48   9.828%   $249.8367   $249.84   $249.85   $249.80  
  Purchase #3 $196.76   5.476%   $207.5346   $207.53   $207.55   $207.50  
  Purchase #4 $33.47   7.806%   $36.0827   $36.08   $36.10   $36.10  
  Purchase #5 $16.91   3.685%   $17.5331   $17.53   $17.55   $17.50  
  Purchase #6 $240.99   6.180%   $255.8832   $255.88   $255.90   $255.90  
  Purchase #7 $6.86   10.739%   $7.5967   $7.60   $7.60   $7.60  
  7 purchase totals = $778.34       $836.2056   $836.20   $836.30   $836.10