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 $50.48   11.279%   $56.1736   $56.17   $56.15   $56.20  
  Purchase #2 $146.35   9.572%   $160.3586   $160.36   $160.35   $160.40  
  Purchase #3 $164.82   11.543%   $183.8452   $183.85   $183.85   $183.80  
  Purchase #4 $56.25   13.119%   $63.6294   $63.63   $63.65   $63.60  
  Purchase #5 $238.64   7.441%   $256.3972   $256.40   $256.40   $256.40  
  Purchase #6 $63.74   3.550%   $66.0028   $66.00   $66.00   $66.00  
  Purchase #7 $158.82   4.403%   $165.8128   $165.81   $165.80   $165.80  
  7 purchase totals = $879.10       $952.2196   $952.22   $952.20   $952.20