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	$88.90	10.474%	$98.2114	$98.21	$98.20	$98.20
Purchase #2	$217.48	9.580%	$238.3146	$238.31	$238.30	$238.30
Purchase #3	$133.92	5.397%	$141.1477	$141.15	$141.15	$141.10
Purchase #4	$133.70	10.725%	$148.0393	$148.04	$148.05	$148.00
Purchase #5	$105.73	3.302%	$109.2212	$109.22	$109.20	$109.20
Purchase #6	$31.75	5.174%	$33.3927	$33.39	$33.40	$33.40
Purchase #7	$115.27	11.762%	$128.8281	$128.83	$128.85	$128.80
7 purchase totals =	$826.75		$897.1550	$897.15	$897.15	$897.00