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 $207.96   11.199%   $231.2494   $231.25   $231.25   $231.20  
  Purchase #2 $171.40   4.234%   $178.6571   $178.66   $178.65   $178.70  
  Purchase #3 $196.72   9.524%   $215.4556   $215.46   $215.45   $215.50  
  Purchase #4 $244.81   6.580%   $260.9185   $260.92   $260.90   $260.90  
  Purchase #5 $51.90   11.629%   $57.9355   $57.94   $57.95   $57.90  
  Purchase #6 $185.48   6.860%   $198.2039   $198.20   $198.20   $198.20  
  Purchase #7 $233.80   3.410%   $241.7726   $241.77   $241.75   $241.80  
  7 purchase totals = $1,292.07       $1,384.1926   $1,384.20   $1,384.15   $1,384.20