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 $247.89   13.719%   $281.898   $281.90   $281.90   $281.90  
  Purchase #2 $156.47   4.136%   $162.9416   $162.94   $162.95   $162.90  
  Purchase #3 $140.93   3.361%   $145.6667   $145.67   $145.65   $145.70  
  Purchase #4 $110.83   13.866%   $126.1977   $126.20   $126.20   $126.20  
  Purchase #5 $26.61   5.305%   $28.0217   $28.02   $28.00   $28.00  
  Purchase #6 $220.77   3.476%   $228.444   $228.44   $228.45   $228.40  
  Purchase #7 $76.25   4.787%   $79.9001   $79.90   $79.90   $79.90  
  7 purchase totals = $979.75       $1,053.0698   $1,053.07   $1,053.05   $1,053.00