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	$26.60	6.278%	$28.2699	$28.27	$28.25	$28.30
Purchase #2	$78.27	5.618%	$82.6672	$82.67	$82.65	$82.70
Purchase #3	$18.77	11.466%	$20.9222	$20.92	$20.90	$20.90
Purchase #4	$119.98	3.199%	$123.8182	$123.82	$123.80	$123.80
Purchase #5	$118.71	13.751%	$135.0338	$135.03	$135.05	$135.00
Purchase #6	$23.74	5.594%	$25.068	$25.07	$25.05	$25.10
Purchase #7	$105.60	10.850%	$117.0576	$117.06	$117.05	$117.10
7 purchase totals =	$491.67		$532.8369	$532.84	$532.75	$532.90