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 $30.95   11.714%   $34.5755   $34.58   $34.60   $34.60  
  Purchase #2 $172.76   9.363%   $188.9355   $188.94   $188.95   $188.90  
  Purchase #3 $231.59   13.464%   $262.7713   $262.77   $262.75   $262.80  
  Purchase #4 $238.76   3.219%   $246.4457   $246.45   $246.45   $246.40  
  Purchase #5 $145.76   5.813%   $154.233   $154.23   $154.25   $154.20  
  Purchase #6 $25.48   4.727%   $26.6844   $26.68   $26.70   $26.70  
  Purchase #7 $134.59   5.498%   $141.9898   $141.99   $142.00   $142.00  
  7 purchase totals = $979.89       $1,055.6352   $1,055.64   $1,055.70   $1,055.60