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 $60.50   3.618%   $62.6889   $62.69   $62.70   $62.70  
  Purchase #2 $71.56   11.307%   $79.6513   $79.65   $79.65   $79.70  
  Purchase #3 $239.97   10.682%   $265.6036   $265.60   $265.60   $265.60  
  Purchase #4 $58.68   4.834%   $61.5166   $61.52   $61.50   $61.50  
  Purchase #5 $234.61   3.237%   $242.2043   $242.20   $242.20   $242.20  
  Purchase #6 $58.77   3.629%   $60.9028   $60.90   $60.90   $60.90  
  Purchase #7 $58.35   8.369%   $63.2333   $63.23   $63.25   $63.20  
  7 purchase totals = $782.44       $835.8008   $835.79   $835.80   $835.80