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 $50.86   6.704%   $54.2697   $54.27   $54.25   $54.30  
  Purchase #2 $231.76   9.705%   $254.2523   $254.25   $254.25   $254.30  
  Purchase #3 $205.71   13.351%   $233.1743   $233.17   $233.15   $233.20  
  Purchase #4 $54.52   5.533%   $57.5366   $57.54   $57.55   $57.50  
  Purchase #5 $246.83   7.748%   $265.9544   $265.95   $265.95   $266.00  
  Purchase #6 $190.28   4.772%   $199.3602   $199.36   $199.35   $199.40  
  Purchase #7 $50.76   10.335%   $56.006   $56.01   $56.00   $56.00  
  7 purchase totals = $1,030.72       $1,120.5535   $1,120.55   $1,120.50   $1,120.70