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	$229.62	13.681%	$261.0343	$261.03	$261.05	$261.00
Purchase #2	$54.32	13.543%	$61.6766	$61.68	$61.70	$61.70
Purchase #3	$169.72	9.571%	$185.9639	$185.96	$185.95	$186.00
Purchase #4	$65.75	10.762%	$72.826	$72.83	$72.85	$72.80
Purchase #5	$11.28	11.198%	$12.5431	$12.54	$12.55	$12.50
Purchase #6	$165.52	12.326%	$185.922	$185.92	$185.90	$185.90
Purchase #7	$195.39	9.304%	$213.5691	$213.57	$213.55	$213.60
7 purchase totals =	$891.60		$993.5350	$993.53	$993.55	$993.50