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	$91.33	5.758%	$96.5888	$96.59	$96.60	$96.60
Purchase #2	$194.41	8.592%	$211.1137	$211.11	$211.10	$211.10
Purchase #3	$137.76	12.465%	$154.9318	$154.93	$154.95	$154.90
Purchase #4	$224.92	13.538%	$255.3697	$255.37	$255.35	$255.40
Purchase #5	$172.86	7.296%	$185.4719	$185.47	$185.45	$185.50
Purchase #6	$70.74	13.183%	$80.0657	$80.07	$80.05	$80.10
Purchase #7	$245.51	11.292%	$273.233	$273.23	$273.25	$273.20
7 purchase totals =	$1,137.53		$1,256.7746	$1,256.77	$1,256.75	$1,256.80