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 $77.96   5.216%   $82.0264   $82.03   $82.05   $82.00  
  Purchase #2 $66.26   3.871%   $68.8249   $68.82   $68.80   $68.80  
  Purchase #3 $116.81   4.583%   $122.1634   $122.16   $122.15   $122.20  
  Purchase #4 $153.95   8.404%   $166.888   $166.89   $166.90   $166.90  
  Purchase #5 $245.65   5.465%   $259.0748   $259.07   $259.05   $259.10  
  Purchase #6 $131.89   13.479%   $149.6675   $149.67   $149.65   $149.70  
  Purchase #7 $205.56   4.775%   $215.3755   $215.38   $215.40   $215.40  
  7 purchase totals = $998.08       $1,064.0205   $1,064.02   $1,064.00   $1,064.10