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 $63.84   6.795%   $68.1779   $68.18   $68.20   $68.20  
  Purchase #2 $210.58   6.681%   $224.6488   $224.65   $224.65   $224.60  
  Purchase #3 $213.82   8.433%   $231.8514   $231.85   $231.85   $231.90  
  Purchase #4 $45.28   4.478%   $47.3076   $47.31   $47.30   $47.30  
  Purchase #5 $153.69   8.402%   $166.603   $166.60   $166.60   $166.60  
  Purchase #6 $57.82   9.648%   $63.3985   $63.40   $63.40   $63.40  
  Purchase #7 $239.72   11.491%   $267.2662   $267.27   $267.25   $267.30  
  7 purchase totals = $984.75       $1,069.2534   $1,069.26   $1,069.25   $1,069.30