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 $185.48   11.711%   $207.2016   $207.20   $207.20   $207.20  
  Purchase #2 $52.87   3.142%   $54.5312   $54.53   $54.55   $54.50  
  Purchase #3 $27.32   8.157%   $29.5485   $29.55   $29.55   $29.50  
  Purchase #4 $162.97   3.268%   $168.2959   $168.30   $168.30   $168.30  
  Purchase #5 $202.93   13.579%   $230.4859   $230.49   $230.50   $230.50  
  Purchase #6 $95.91   8.119%   $103.6969   $103.70   $103.70   $103.70  
  Purchase #7 $208.80   8.473%   $226.4916   $226.49   $226.50   $226.50  
  7 purchase totals = $936.28       $1,020.2516   $1,020.26   $1,020.30   $1,020.20