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 $228.82   7.153%   $245.1875   $245.19   $245.20   $245.20  
  Purchase #2 $190.40   12.840%   $214.8474   $214.85   $214.85   $214.80  
  Purchase #3 $24.25   11.837%   $27.1205   $27.12   $27.10   $27.10  
  Purchase #4 $207.95   5.313%   $218.9984   $219.00   $219.00   $219.00  
  Purchase #5 $94.30   8.374%   $102.1967   $102.20   $102.20   $102.20  
  Purchase #6 $157.54   12.803%   $177.7098   $177.71   $177.70   $177.70  
  Purchase #7 $9.60   12.602%   $10.8098   $10.81   $10.80   $10.80  
  7 purchase totals = $912.86       $996.8701   $996.88   $996.85   $996.80