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 $168.61   5.122%   $177.2462   $177.25   $177.25   $177.20  
  Purchase #2 $41.87   6.354%   $44.5304   $44.53   $44.55   $44.50  
  Purchase #3 $107.75   5.513%   $113.6903   $113.69   $113.70   $113.70  
  Purchase #4 $206.43   4.567%   $215.8577   $215.86   $215.85   $215.90  
  Purchase #5 $223.55   11.266%   $248.7351   $248.74   $248.75   $248.70  
  Purchase #6 $99.67   3.310%   $102.9691   $102.97   $102.95   $103.00  
  Purchase #7 $111.72   8.102%   $120.7716   $120.77   $120.75   $120.80  
  7 purchase totals = $959.60       $1,023.8004   $1,023.81   $1,023.80   $1,023.80