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 $59.99   10.244%   $66.1354   $66.14   $66.15   $66.10  
  Purchase #2 $144.64   6.818%   $154.5016   $154.50   $154.50   $154.50  
  Purchase #3 $41.79   3.331%   $43.182   $43.18   $43.20   $43.20  
  Purchase #4 $187.54   9.844%   $206.0014   $206.00   $206.00   $206.00  
  Purchase #5 $50.26   13.212%   $56.9004   $56.90   $56.90   $56.90  
  Purchase #6 $206.56   7.484%   $222.019   $222.02   $222.00   $222.00  
  Purchase #7 $78.28   6.792%   $83.5968   $83.60   $83.60   $83.60  
  7 purchase totals = $769.06       $832.3366   $832.34   $832.35   $832.30