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 $23.59   13.731%   $26.8291   $26.83   $26.85   $26.80  
  Purchase #2 $134.77   6.218%   $143.15   $143.15   $143.15   $143.20  
  Purchase #3 $131.76   5.196%   $138.6062   $138.61   $138.60   $138.60  
  Purchase #4 $158.39   10.667%   $175.2855   $175.29   $175.30   $175.30  
  Purchase #5 $160.99   3.370%   $166.4154   $166.42   $166.40   $166.40  
  Purchase #6 $163.68   4.472%   $170.9998   $171.00   $171.00   $171.00  
  Purchase #7 $211.77   13.171%   $239.6622   $239.66   $239.65   $239.70  
  7 purchase totals = $984.95       $1,060.9482   $1,060.96   $1,060.95   $1,061.00