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 $57.66   6.590%   $61.4598   $61.46   $61.45   $61.50  
  Purchase #2 $117.96   5.409%   $124.3405   $124.34   $124.35   $124.30  
  Purchase #3 $240.95   10.723%   $266.7871   $266.79   $266.80   $266.80  
  Purchase #4 $44.51   8.289%   $48.1994   $48.20   $48.20   $48.20  
  Purchase #5 $157.81   12.576%   $177.6562   $177.66   $177.65   $177.70  
  Purchase #6 $96.33   12.413%   $108.2874   $108.29   $108.30   $108.30  
  Purchase #7 $56.70   6.112%   $60.1655   $60.17   $60.15   $60.20  
  7 purchase totals = $771.92       $846.8959   $846.91   $846.90   $847.00