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 $65.38   3.383%   $67.5918   $67.59   $67.60   $67.60  
  Purchase #2 $230.85   11.139%   $256.5644   $256.56   $256.55   $256.60  
  Purchase #3 $212.29   3.628%   $219.9919   $219.99   $220.00   $220.00  
  Purchase #4 $174.49   6.794%   $186.3449   $186.34   $186.35   $186.30  
  Purchase #5 $59.82   6.474%   $63.6927   $63.69   $63.70   $63.70  
  Purchase #6 $103.44   10.180%   $113.9702   $113.97   $113.95   $114.00  
  Purchase #7 $219.61   3.863%   $228.0935   $228.09   $228.10   $228.10  
  7 purchase totals = $1,065.88       $1,136.2494   $1,136.23   $1,136.25   $1,136.30