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 $72.53   5.362%   $76.4191   $76.42   $76.40   $76.40  
  Purchase #2 $171.65   12.570%   $193.2264   $193.23   $193.25   $193.20  
  Purchase #3 $177.99   6.564%   $189.6733   $189.67   $189.65   $189.70  
  Purchase #4 $193.83   5.387%   $204.2716   $204.27   $204.25   $204.30  
  Purchase #5 $73.48   8.614%   $79.8096   $79.81   $79.80   $79.80  
  Purchase #6 $249.83   5.330%   $263.1459   $263.15   $263.15   $263.10  
  Purchase #7 $20.72   10.232%   $22.8401   $22.84   $22.85   $22.80  
  7 purchase totals = $960.03       $1,029.3860   $1,029.39   $1,029.35   $1,029.30