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 $57.95   13.778%   $65.9344   $65.93   $65.95   $65.90  
  Purchase #2 $231.37   4.841%   $242.5706   $242.57   $242.55   $242.60  
  Purchase #3 $114.62   8.450%   $124.3054   $124.31   $124.30   $124.30  
  Purchase #4 $162.75   6.773%   $173.7731   $173.77   $173.75   $173.80  
  Purchase #5 $159.35   5.277%   $167.7589   $167.76   $167.75   $167.80  
  Purchase #6 $160.70   10.599%   $177.7326   $177.73   $177.75   $177.70  
  Purchase #7 $152.37   13.280%   $172.6047   $172.60   $172.60   $172.60  
  7 purchase totals = $1,039.11       $1,124.6797   $1,124.67   $1,124.65   $1,124.70