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	$104.79	6.648%	$111.7564	$111.76	$111.75	$111.80
Purchase #2	$200.46	11.116%	$222.7431	$222.74	$222.75	$222.70
Purchase #3	$34.44	8.764%	$37.4583	$37.46	$37.45	$37.50
Purchase #4	$59.40	6.522%	$63.2741	$63.27	$63.25	$63.30
Purchase #5	$117.59	5.693%	$124.2844	$124.28	$124.30	$124.30
Purchase #6	$82.48	11.214%	$91.7293	$91.73	$91.75	$91.70
Purchase #7	$159.72	7.425%	$171.5792	$171.58	$171.60	$171.60
7 purchase totals =	$758.88		$822.8248	$822.82	$822.85	$822.90