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	$6.73	12.712%	$7.5855	$7.59	$7.60	$7.60
Purchase #2	$229.72	8.257%	$248.688	$248.69	$248.70	$248.70
Purchase #3	$225.37	13.394%	$255.5561	$255.56	$255.55	$255.60
Purchase #4	$245.44	9.638%	$269.0955	$269.10	$269.10	$269.10
Purchase #5	$144.78	6.323%	$153.9344	$153.93	$153.95	$153.90
Purchase #6	$143.96	5.489%	$151.862	$151.86	$151.85	$151.90
Purchase #7	$117.74	11.719%	$131.538	$131.54	$131.55	$131.50
7 purchase totals =	$1,113.74		$1,218.2595	$1,218.27	$1,218.30	$1,218.30