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	$45.84	9.709%	$50.2906	$50.29	$50.30	$50.30
Purchase #2	$59.30	5.267%	$62.4233	$62.42	$62.40	$62.40
Purchase #3	$89.85	11.178%	$99.8934	$99.89	$99.90	$99.90
Purchase #4	$113.26	5.545%	$119.5403	$119.54	$119.55	$119.50
Purchase #5	$46.82	11.567%	$52.2357	$52.24	$52.25	$52.20
Purchase #6	$25.39	10.577%	$28.0755	$28.08	$28.10	$28.10
Purchase #7	$161.73	7.588%	$174.0021	$174.00	$174.00	$174.00
7 purchase totals =	$542.19		$586.4609	$586.46	$586.50	$586.40