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 $214.99   5.558%   $226.9391   $226.94   $226.95   $226.90  
  Purchase #2 $51.42   10.211%   $56.6705   $56.67   $56.65   $56.70  
  Purchase #3 $48.28   11.154%   $53.6652   $53.67   $53.65   $53.70  
  Purchase #4 $168.88   8.570%   $183.353   $183.35   $183.35   $183.40  
  Purchase #5 $126.26   6.485%   $134.448   $134.45   $134.45   $134.40  
  Purchase #6 $54.49   4.165%   $56.7595   $56.76   $56.75   $56.80  
  Purchase #7 $152.64   9.133%   $166.5806   $166.58   $166.60   $166.60  
  7 purchase totals = $816.96       $878.4159   $878.42   $878.40   $878.50