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 $7.51   10.108%   $8.2691   $8.27   $8.25   $8.30  
  Purchase #2 $60.52   3.585%   $62.6896   $62.69   $62.70   $62.70  
  Purchase #3 $173.99   13.699%   $197.8249   $197.82   $197.80   $197.80  
  Purchase #4 $200.51   8.250%   $217.0521   $217.05   $217.05   $217.10  
  Purchase #5 $185.31   9.214%   $202.3845   $202.38   $202.40   $202.40  
  Purchase #6 $86.78   10.788%   $96.1418   $96.14   $96.15   $96.10  
  Purchase #7 $213.36   8.698%   $231.9181   $231.92   $231.90   $231.90  
  7 purchase totals = $927.98       $1,016.2801   $1,016.27   $1,016.25   $1,016.30