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	$166.82	6.415%	$177.5215	$177.52	$177.50	$177.50
Purchase #2	$172.52	10.575%	$190.764	$190.76	$190.75	$190.80
Purchase #3	$186.56	10.319%	$205.8111	$205.81	$205.80	$205.80
Purchase #4	$110.82	11.670%	$123.7527	$123.75	$123.75	$123.80
Purchase #5	$204.95	5.821%	$216.8801	$216.88	$216.90	$216.90
Purchase #6	$182.33	5.807%	$192.9179	$192.92	$192.90	$192.90
Purchase #7	$159.59	4.220%	$166.3247	$166.32	$166.30	$166.30
7 purchase totals =	$1,183.59		$1,273.9720	$1,273.96	$1,273.90	$1,274.00