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 $120.44   3.115%   $124.1917   $124.19   $124.20   $124.20  
  Purchase #2 $213.49   9.156%   $233.0371   $233.04   $233.05   $233.00  
  Purchase #3 $19.92   11.838%   $22.2781   $22.28   $22.30   $22.30  
  Purchase #4 $162.55   7.264%   $174.3576   $174.36   $174.35   $174.40  
  Purchase #5 $163.25   10.871%   $180.9969   $181.00   $181.00   $181.00  
  Purchase #6 $239.67   5.724%   $253.3887   $253.39   $253.40   $253.40  
  Purchase #7 $149.91   10.153%   $165.1304   $165.13   $165.15   $165.10  
  7 purchase totals = $1,069.23       $1,153.3805   $1,153.39   $1,153.45   $1,153.40