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	$29.66	12.296%	$33.307	$33.31	$33.30	$33.30
Purchase #2	$238.81	13.719%	$271.5723	$271.57	$271.55	$271.60
Purchase #3	$183.28	3.480%	$189.6581	$189.66	$189.65	$189.70
Purchase #4	$190.31	3.110%	$196.2286	$196.23	$196.25	$196.20
Purchase #5	$177.81	6.370%	$189.1365	$189.14	$189.15	$189.10
Purchase #6	$20.41	10.128%	$22.4771	$22.48	$22.50	$22.50
Purchase #7	$85.66	7.233%	$91.8558	$91.86	$91.85	$91.90
7 purchase totals =	$925.94		$994.2354	$994.25	$994.25	$994.30