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 $250.96   8.357%   $271.9327   $271.93   $271.95   $271.90  
  Purchase #2 $56.99   8.757%   $61.9806   $61.98   $62.00   $62.00  
  Purchase #3 $5.74   5.267%   $6.0423   $6.04   $6.05   $6.00  
  Purchase #4 $187.35   11.732%   $209.3299   $209.33   $209.35   $209.30  
  Purchase #5 $243.86   3.434%   $252.2342   $252.23   $252.25   $252.20  
  Purchase #6 $89.44   7.747%   $96.3689   $96.37   $96.35   $96.40  
  Purchase #7 $47.61   10.677%   $52.6933   $52.69   $52.70   $52.70  
  7 purchase totals = $881.95       $950.5819   $950.57   $950.65   $950.50