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	$75.46	3.874%	$78.3833	$78.38	$78.40	$78.40
Purchase #2	$220.86	11.801%	$246.9237	$246.92	$246.90	$246.90
Purchase #3	$241.84	5.145%	$254.2827	$254.28	$254.30	$254.30
Purchase #4	$158.37	7.338%	$169.9912	$169.99	$170.00	$170.00
Purchase #5	$91.95	8.233%	$99.5202	$99.52	$99.50	$99.50
Purchase #6	$58.92	7.520%	$63.3508	$63.35	$63.35	$63.40
Purchase #7	$204.71	12.301%	$229.8914	$229.89	$229.90	$229.90
7 purchase totals =	$1,052.11		$1,142.3433	$1,142.33	$1,142.35	$1,142.40