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 $60.86   13.193%   $68.8893   $68.89   $68.90   $68.90  
  Purchase #2 $49.96   4.394%   $52.1552   $52.16   $52.15   $52.20  
  Purchase #3 $62.57   3.751%   $64.917   $64.92   $64.90   $64.90  
  Purchase #4 $76.78   10.784%   $85.06   $85.06   $85.05   $85.10  
  Purchase #5 $118.59   3.547%   $122.7964   $122.80   $122.80   $122.80  
  Purchase #6 $134.51   3.448%   $139.1479   $139.15   $139.15   $139.10  
  Purchase #7 $47.58   6.227%   $50.5428   $50.54   $50.55   $50.50  
  7 purchase totals = $550.85       $583.5086   $583.52   $583.50   $583.50