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 $138.65   11.495%   $154.5878   $154.59   $154.60   $154.60  
  Purchase #2 $49.93   13.546%   $56.6935   $56.69   $56.70   $56.70  
  Purchase #3 $111.90   6.551%   $119.2306   $119.23   $119.25   $119.20  
  Purchase #4 $72.80   5.195%   $76.582   $76.58   $76.60   $76.60  
  Purchase #5 $77.53   11.206%   $86.218   $86.22   $86.20   $86.20  
  Purchase #6 $165.34   9.782%   $181.5136   $181.51   $181.50   $181.50  
  Purchase #7 $94.61   13.317%   $107.2092   $107.21   $107.20   $107.20  
  7 purchase totals = $710.76       $782.0347   $782.03   $782.05   $782.00