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	$84.37	6.350%	$89.7275	$89.73	$89.75	$89.70
Purchase #2	$104.63	6.714%	$111.6549	$111.65	$111.65	$111.70
Purchase #3	$82.27	4.469%	$85.9466	$85.95	$85.95	$85.90
Purchase #4	$149.69	13.865%	$170.4445	$170.44	$170.45	$170.40
Purchase #5	$178.37	5.414%	$188.027	$188.03	$188.05	$188.00
Purchase #6	$41.48	11.473%	$46.239	$46.24	$46.25	$46.20
Purchase #7	$140.65	7.618%	$151.3647	$151.36	$151.35	$151.40
7 purchase totals =	$781.46		$843.4042	$843.40	$843.45	$843.30