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	$34.39	3.289%	$35.5211	$35.52	$35.50	$35.50
Purchase #2	$208.86	9.793%	$229.3137	$229.31	$229.30	$229.30
Purchase #3	$118.83	5.556%	$125.4322	$125.43	$125.45	$125.40
Purchase #4	$125.79	11.657%	$140.4533	$140.45	$140.45	$140.50
Purchase #5	$229.44	11.519%	$255.8692	$255.87	$255.85	$255.90
Purchase #6	$229.56	11.461%	$255.8699	$255.87	$255.85	$255.90
Purchase #7	$187.25	11.848%	$209.4354	$209.44	$209.45	$209.40
7 purchase totals =	$1,134.12		$1,251.8948	$1,251.89	$1,251.85	$1,251.90