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 $76.56   10.557%   $84.6424   $84.64   $84.65   $84.60  
  Purchase #2 $241.59   13.194%   $273.4654   $273.47   $273.45   $273.50  
  Purchase #3 $144.42   12.863%   $162.9967   $163.00   $163.00   $163.00  
  Purchase #4 $58.91   5.615%   $62.2178   $62.22   $62.20   $62.20  
  Purchase #5 $223.71   13.197%   $253.233   $253.23   $253.25   $253.20  
  Purchase #6 $99.59   9.546%   $109.0969   $109.10   $109.10   $109.10  
  Purchase #7 $83.34   3.801%   $86.5078   $86.51   $86.50   $86.50  
  7 purchase totals = $928.12       $1,032.1600   $1,032.17   $1,032.15   $1,032.10