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 $243.84   10.553%   $269.5724   $269.57   $269.55   $269.60  
  Purchase #2 $56.83   10.511%   $62.8034   $62.80   $62.80   $62.80  
  Purchase #3 $166.31   8.473%   $180.4014   $180.40   $180.40   $180.40  
  Purchase #4 $13.57   12.433%   $15.2572   $15.26   $15.25   $15.30  
  Purchase #5 $58.76   6.237%   $62.4249   $62.42   $62.40   $62.40  
  Purchase #6 $191.64   8.839%   $208.5791   $208.58   $208.60   $208.60  
  Purchase #7 $92.56   4.440%   $96.6697   $96.67   $96.65   $96.70  
  7 purchase totals = $823.51       $895.7081   $895.70   $895.65   $895.80