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 $226.95   12.221%   $254.6856   $254.69   $254.70   $254.70  
  Purchase #2 $169.39   12.648%   $190.8144   $190.81   $190.80   $190.80  
  Purchase #3 $23.64   4.344%   $24.6669   $24.67   $24.65   $24.70  
  Purchase #4 $39.72   9.621%   $43.5415   $43.54   $43.55   $43.50  
  Purchase #5 $68.43   3.638%   $70.9195   $70.92   $70.90   $70.90  
  Purchase #6 $238.31   4.545%   $249.1412   $249.14   $249.15   $249.10  
  Purchase #7 $166.70   8.738%   $181.2662   $181.27   $181.25   $181.30  
  7 purchase totals = $933.14       $1,015.0353   $1,015.04   $1,015.00   $1,015.00