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	$17.31	3.454%	$17.9079	$17.91	$17.90	$17.90
Purchase #2	$94.64	4.682%	$99.071	$99.07	$99.05	$99.10
Purchase #3	$37.92	12.858%	$42.7958	$42.80	$42.80	$42.80
Purchase #4	$115.78	13.402%	$131.2968	$131.30	$131.30	$131.30
Purchase #5	$83.80	6.669%	$89.3886	$89.39	$89.40	$89.40
Purchase #6	$179.82	5.103%	$188.9962	$189.00	$189.00	$189.00
Purchase #7	$242.61	6.213%	$257.6834	$257.68	$257.70	$257.70
7 purchase totals =	$771.88		$827.1397	$827.15	$827.15	$827.20