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 $54.43   13.222%   $61.6267   $61.63   $61.65   $61.60  
  Purchase #2 $40.85   8.583%   $44.3562   $44.36   $44.35   $44.40  
  Purchase #3 $161.27   8.555%   $175.0666   $175.07   $175.05   $175.10  
  Purchase #4 $196.84   12.378%   $221.2049   $221.20   $221.20   $221.20  
  Purchase #5 $64.85   6.112%   $68.8136   $68.81   $68.80   $68.80  
  Purchase #6 $60.28   4.724%   $63.1276   $63.13   $63.15   $63.10  
  Purchase #7 $12.70   11.173%   $14.119   $14.12   $14.10   $14.10  
  7 purchase totals = $591.22       $648.3146   $648.32   $648.30   $648.30