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 $248.72   8.160%   $269.0156   $269.02   $269.00   $269.00  
  Purchase #2 $160.53   9.356%   $175.5492   $175.55   $175.55   $175.50  
  Purchase #3 $108.91   6.692%   $116.1983   $116.20   $116.20   $116.20  
  Purchase #4 $208.33   3.431%   $215.4778   $215.48   $215.50   $215.50  
  Purchase #5 $16.33   6.330%   $17.3637   $17.36   $17.35   $17.40  
  Purchase #6 $181.91   6.225%   $193.2339   $193.23   $193.25   $193.20  
  Purchase #7 $61.75   6.567%   $65.8051   $65.81   $65.80   $65.80  
  7 purchase totals = $986.48       $1,052.6436   $1,052.65   $1,052.65   $1,052.60