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 $89.92   4.773%   $94.2119   $94.21   $94.20   $94.20  
  Purchase #2 $203.68   9.336%   $222.6956   $222.70   $222.70   $222.70  
  Purchase #3 $170.83   10.411%   $188.6151   $188.62   $188.60   $188.60  
  Purchase #4 $154.84   7.614%   $166.6295   $166.63   $166.65   $166.60  
  Purchase #5 $172.43   7.839%   $185.9468   $185.95   $185.95   $185.90  
  Purchase #6 $245.55   9.607%   $269.14   $269.14   $269.15   $269.10  
  Purchase #7 $227.34   5.130%   $239.0025   $239.00   $239.00   $239.00  
  7 purchase totals = $1,264.59       $1,366.2414   $1,366.25   $1,366.25   $1,366.10