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 $217.35   12.757%   $245.0773   $245.08   $245.10   $245.10  
  Purchase #2 $181.86   6.348%   $193.4045   $193.40   $193.40   $193.40  
  Purchase #3 $240.45   6.701%   $256.5626   $256.56   $256.55   $256.60  
  Purchase #4 $65.80   6.614%   $70.152   $70.15   $70.15   $70.20  
  Purchase #5 $29.94   3.268%   $30.9184   $30.92   $30.90   $30.90  
  Purchase #6 $144.87   4.509%   $151.4022   $151.40   $151.40   $151.40  
  Purchase #7 $70.58   5.515%   $74.4725   $74.47   $74.45   $74.50  
  7 purchase totals = $950.85       $1,021.9895   $1,021.98   $1,021.95   $1,022.10