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 $68.77   9.365%   $75.2103   $75.21   $75.20   $75.20  
  Purchase #2 $107.65   8.873%   $117.2018   $117.20   $117.20   $117.20  
  Purchase #3 $250.40   8.411%   $271.4611   $271.46   $271.45   $271.50  
  Purchase #4 $96.65   8.715%   $105.073   $105.07   $105.05   $105.10  
  Purchase #5 $125.25   7.233%   $134.3093   $134.31   $134.30   $134.30  
  Purchase #6 $58.48   12.147%   $65.5836   $65.58   $65.60   $65.60  
  Purchase #7 $106.68   12.118%   $119.6075   $119.61   $119.60   $119.60  
  7 purchase totals = $813.88       $888.4466   $888.44   $888.40   $888.50