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 $184.89   10.355%   $204.0354   $204.04   $204.05   $204.00  
  Purchase #2 $120.89   9.369%   $132.2162   $132.22   $132.20   $132.20  
  Purchase #3 $25.76   3.439%   $26.6459   $26.65   $26.65   $26.60  
  Purchase #4 $54.49   9.377%   $59.5995   $59.60   $59.60   $59.60  
  Purchase #5 $70.86   4.369%   $73.9559   $73.96   $73.95   $74.00  
  Purchase #6 $166.62   10.632%   $184.335   $184.34   $184.35   $184.30  
  Purchase #7 $155.40   4.314%   $162.104   $162.10   $162.10   $162.10  
  7 purchase totals = $778.91       $842.8919   $842.91   $842.90   $842.80