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 $170.46   7.699%   $183.5837   $183.58   $183.60   $183.60  
  Purchase #2 $205.95   11.142%   $228.8969   $228.90   $228.90   $228.90  
  Purchase #3 $58.25   10.492%   $64.3616   $64.36   $64.35   $64.40  
  Purchase #4 $168.75   3.385%   $174.4622   $174.46   $174.45   $174.50  
  Purchase #5 $83.96   3.410%   $86.823   $86.82   $86.80   $86.80  
  Purchase #6 $197.92   8.557%   $214.856   $214.86   $214.85   $214.90  
  Purchase #7 $13.40   3.830%   $13.9132   $13.91   $13.90   $13.90  
  7 purchase totals = $898.69       $966.8966   $966.89   $966.85   $967.00