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	$166.61	6.420%	$177.3064	$177.31	$177.30	$177.30
Purchase #2	$201.50	13.463%	$228.6279	$228.63	$228.65	$228.60
Purchase #3	$69.92	12.841%	$78.8984	$78.90	$78.90	$78.90
Purchase #4	$180.93	11.154%	$201.1109	$201.11	$201.10	$201.10
Purchase #5	$192.86	13.709%	$219.2992	$219.30	$219.30	$219.30
Purchase #6	$51.34	12.756%	$57.8889	$57.89	$57.90	$57.90
Purchase #7	$128.37	11.228%	$142.7834	$142.78	$142.80	$142.80
7 purchase totals =	$991.53		$1,105.9151	$1,105.92	$1,105.95	$1,105.90