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 $181.48   13.616%   $206.1903   $206.19   $206.20   $206.20  
  Purchase #2 $166.39   5.189%   $175.024   $175.02   $175.00   $175.00  
  Purchase #3 $91.43   4.312%   $95.3725   $95.37   $95.35   $95.40  
  Purchase #4 $82.90   6.689%   $88.4452   $88.45   $88.45   $88.40  
  Purchase #5 $226.46   5.656%   $239.2686   $239.27   $239.25   $239.30  
  Purchase #6 $238.27   3.726%   $247.1479   $247.15   $247.15   $247.10  
  Purchase #7 $166.91   5.456%   $176.0166   $176.02   $176.00   $176.00  
  7 purchase totals = $1,153.84       $1,227.4651   $1,227.47   $1,227.40   $1,227.40