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	$74.32	8.615%	$80.7227	$80.72	$80.70	$80.70
Purchase #2	$39.99	4.823%	$41.9187	$41.92	$41.90	$41.90
Purchase #3	$249.92	11.498%	$278.6558	$278.66	$278.65	$278.70
Purchase #4	$241.45	9.616%	$264.6678	$264.67	$264.65	$264.70
Purchase #5	$57.33	4.430%	$59.8697	$59.87	$59.85	$59.90
Purchase #6	$92.91	13.557%	$105.5058	$105.51	$105.50	$105.50
Purchase #7	$101.75	12.402%	$114.369	$114.37	$114.35	$114.40
7 purchase totals =	$857.67		$945.7095	$945.72	$945.60	$945.80