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 $53.48   13.724%   $60.8196   $60.82   $60.80   $60.80  
  Purchase #2 $15.85   6.642%   $16.9028   $16.90   $16.90   $16.90  
  Purchase #3 $83.29   4.810%   $87.2962   $87.30   $87.30   $87.30  
  Purchase #4 $112.57   4.320%   $117.433   $117.43   $117.45   $117.40  
  Purchase #5 $145.57   8.652%   $158.1647   $158.16   $158.15   $158.20  
  Purchase #6 $159.91   9.835%   $175.6371   $175.64   $175.65   $175.60  
  Purchase #7 $9.51   10.671%   $10.5248   $10.52   $10.50   $10.50  
  7 purchase totals = $580.18       $626.7782   $626.77   $626.75   $626.70