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 $57.67   5.487%   $60.8344   $60.83   $60.85   $60.80  
  Purchase #2 $139.62   10.808%   $154.7101   $154.71   $154.70   $154.70  
  Purchase #3 $208.69   5.293%   $219.736   $219.74   $219.75   $219.70  
  Purchase #4 $171.96   3.139%   $177.3578   $177.36   $177.35   $177.40  
  Purchase #5 $151.48   6.759%   $161.7185   $161.72   $161.70   $161.70  
  Purchase #6 $117.95   4.286%   $123.0053   $123.01   $123.00   $123.00  
  Purchase #7 $48.70   4.513%   $50.8978   $50.90   $50.90   $50.90  
  7 purchase totals = $896.07       $948.2599   $948.27   $948.25   $948.20