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 $63.83   7.274%   $68.473   $68.47   $68.45   $68.50  
  Purchase #2 $159.74   10.613%   $176.6932   $176.69   $176.70   $176.70  
  Purchase #3 $156.52   11.255%   $174.1363   $174.14   $174.15   $174.10  
  Purchase #4 $40.56   10.428%   $44.7896   $44.79   $44.80   $44.80  
  Purchase #5 $186.45   10.662%   $206.3293   $206.33   $206.35   $206.30  
  Purchase #6 $98.62   8.618%   $107.1191   $107.12   $107.10   $107.10  
  Purchase #7 $228.62   8.833%   $248.814   $248.81   $248.80   $248.80  
  7 purchase totals = $934.34       $1,026.3545   $1,026.35   $1,026.35   $1,026.30