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 $153.26   7.855%   $165.2986   $165.30   $165.30   $165.30  
  Purchase #2 $207.42   8.844%   $225.7642   $225.76   $225.75   $225.80  
  Purchase #3 $76.54   7.283%   $82.1144   $82.11   $82.10   $82.10  
  Purchase #4 $14.43   7.688%   $15.5394   $15.54   $15.55   $15.50  
  Purchase #5 $125.63   13.170%   $142.1755   $142.18   $142.20   $142.20  
  Purchase #6 $190.87   8.657%   $207.3936   $207.39   $207.40   $207.40  
  Purchase #7 $95.71   11.413%   $106.6334   $106.63   $106.65   $106.60  
  7 purchase totals = $863.86       $944.9191   $944.91   $944.95   $944.90