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	$29.68	7.557%	$31.9229	$31.92	$31.90	$31.90
Purchase #2	$42.90	6.275%	$45.592	$45.59	$45.60	$45.60
Purchase #3	$156.26	11.281%	$173.8877	$173.89	$173.90	$173.90
Purchase #4	$173.41	12.779%	$195.5701	$195.57	$195.55	$195.60
Purchase #5	$214.87	11.496%	$239.5715	$239.57	$239.55	$239.60
Purchase #6	$99.69	3.607%	$103.2858	$103.29	$103.30	$103.30
Purchase #7	$79.72	4.127%	$83.01	$83.01	$83.00	$83.00
7 purchase totals =	$796.53		$872.8400	$872.84	$872.80	$872.90