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	$230.39	3.373%	$238.1611	$238.16	$238.15	$238.20
Purchase #2	$87.26	10.487%	$96.411	$96.41	$96.40	$96.40
Purchase #3	$142.78	12.330%	$160.3848	$160.38	$160.40	$160.40
Purchase #4	$235.88	9.263%	$257.7296	$257.73	$257.75	$257.70
Purchase #5	$81.87	9.329%	$89.5077	$89.51	$89.50	$89.50
Purchase #6	$123.36	6.590%	$131.4894	$131.49	$131.50	$131.50
Purchase #7	$35.92	7.517%	$38.6201	$38.62	$38.60	$38.60
7 purchase totals =	$937.46		$1,012.3037	$1,012.30	$1,012.30	$1,012.30