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	$106.43	8.565%	$115.5457	$115.55	$115.55	$115.50
Purchase #2	$250.87	10.236%	$276.5491	$276.55	$276.55	$276.50
Purchase #3	$67.76	6.340%	$72.056	$72.06	$72.05	$72.10
Purchase #4	$79.95	11.173%	$88.8828	$88.88	$88.90	$88.90
Purchase #5	$78.55	9.656%	$86.1348	$86.13	$86.15	$86.10
Purchase #6	$40.51	12.410%	$45.5373	$45.54	$45.55	$45.50
Purchase #7	$144.41	9.683%	$158.3932	$158.39	$158.40	$158.40
7 purchase totals =	$768.48		$843.0989	$843.10	$843.15	$843.00