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 $96.59   5.342%   $101.7498   $101.75   $101.75   $101.70  
  Purchase #2 $222.33   11.785%   $248.5316   $248.53   $248.55   $248.50  
  Purchase #3 $154.37   6.540%   $164.4658   $164.47   $164.45   $164.50  
  Purchase #4 $55.91   12.724%   $63.024   $63.02   $63.00   $63.00  
  Purchase #5 $24.97   9.736%   $27.4011   $27.40   $27.40   $27.40  
  Purchase #6 $148.64   12.119%   $166.6537   $166.65   $166.65   $166.70  
  Purchase #7 $99.69   10.572%   $110.2292   $110.23   $110.25   $110.20  
  7 purchase totals = $802.50       $882.0552   $882.05   $882.05   $882.00