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	$162.79	3.275%	$168.1214	$168.12	$168.10	$168.10
Purchase #2	$157.46	10.243%	$173.5886	$173.59	$173.60	$173.60
Purchase #3	$122.72	13.511%	$139.3007	$139.30	$139.30	$139.30
Purchase #4	$183.36	10.214%	$202.0884	$202.09	$202.10	$202.10
Purchase #5	$216.38	13.358%	$245.284	$245.28	$245.30	$245.30
Purchase #6	$106.58	4.501%	$111.3772	$111.38	$111.40	$111.40
Purchase #7	$24.88	8.851%	$27.0821	$27.08	$27.10	$27.10
7 purchase totals =	$974.17		$1,066.8424	$1,066.84	$1,066.90	$1,066.90