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 $188.72   11.554%   $210.5247   $210.52   $210.50   $210.50  
  Purchase #2 $52.28   10.866%   $57.9607   $57.96   $57.95   $58.00  
  Purchase #3 $158.57   12.341%   $178.1391   $178.14   $178.15   $178.10  
  Purchase #4 $206.90   5.294%   $217.8533   $217.85   $217.85   $217.90  
  Purchase #5 $8.37   13.451%   $9.4958   $9.50   $9.50   $9.50  
  Purchase #6 $157.51   10.283%   $173.7068   $173.71   $173.70   $173.70  
  Purchase #7 $179.44   3.745%   $186.16   $186.16   $186.15   $186.20  
  7 purchase totals = $951.79       $1,033.8404   $1,033.84   $1,033.80   $1,033.90