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 $226.94   8.374%   $245.944   $245.94   $245.95   $245.90  
  Purchase #2 $156.63   3.869%   $162.69   $162.69   $162.70   $162.70  
  Purchase #3 $106.39   10.685%   $117.7578   $117.76   $117.75   $117.80  
  Purchase #4 $24.50   5.281%   $25.7938   $25.79   $25.80   $25.80  
  Purchase #5 $13.36   7.186%   $14.32   $14.32   $14.30   $14.30  
  Purchase #6 $92.64   3.798%   $96.1585   $96.16   $96.15   $96.20  
  Purchase #7 $113.86   10.389%   $125.6889   $125.69   $125.70   $125.70  
  7 purchase totals = $734.32       $788.3530   $788.35   $788.35   $788.40