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 $24.70   7.395%   $26.5266   $26.53   $26.55   $26.50  
  Purchase #2 $248.96   9.598%   $272.8552   $272.86   $272.85   $272.90  
  Purchase #3 $170.27   3.235%   $175.7782   $175.78   $175.80   $175.80  
  Purchase #4 $97.52   13.455%   $110.6413   $110.64   $110.65   $110.60  
  Purchase #5 $246.70   13.474%   $279.9404   $279.94   $279.95   $279.90  
  Purchase #6 $44.42   5.509%   $46.8671   $46.87   $46.85   $46.90  
  Purchase #7 $71.93   5.805%   $76.1055   $76.11   $76.10   $76.10  
  7 purchase totals = $904.50       $988.7143   $988.73   $988.75   $988.70