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	$249.65	7.848%	$269.2425	$269.24	$269.25	$269.20
Purchase #2	$192.87	9.572%	$211.3315	$211.33	$211.35	$211.30
Purchase #3	$51.70	10.146%	$56.9455	$56.95	$56.95	$56.90
Purchase #4	$103.75	7.447%	$111.4763	$111.48	$111.50	$111.50
Purchase #5	$209.30	9.645%	$229.487	$229.49	$229.50	$229.50
Purchase #6	$101.71	11.473%	$113.3792	$113.38	$113.40	$113.40
Purchase #7	$216.30	6.285%	$229.8945	$229.89	$229.90	$229.90
7 purchase totals =	$1,125.28		$1,221.7565	$1,221.76	$1,221.85	$1,221.70