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 $207.58   9.205%   $226.6877   $226.69   $226.70   $226.70  
  Purchase #2 $161.30   3.357%   $166.7148   $166.71   $166.70   $166.70  
  Purchase #3 $62.88   3.298%   $64.9538   $64.95   $64.95   $65.00  
  Purchase #4 $79.49   3.764%   $82.482   $82.48   $82.50   $82.50  
  Purchase #5 $5.34   5.654%   $5.6419   $5.64   $5.65   $5.60  
  Purchase #6 $243.49   4.685%   $254.8975   $254.90   $254.90   $254.90  
  Purchase #7 $81.27   6.250%   $86.3494   $86.35   $86.35   $86.30  
  7 purchase totals = $841.35       $887.7271   $887.72   $887.75   $887.70