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	$139.35	5.175%	$146.5614	$146.56	$146.55	$146.60
Purchase #2	$39.96	8.506%	$43.359	$43.36	$43.35	$43.40
Purchase #3	$11.35	12.370%	$12.754	$12.75	$12.75	$12.80
Purchase #4	$247.72	8.406%	$268.5433	$268.54	$268.55	$268.50
Purchase #5	$204.32	8.865%	$222.433	$222.43	$222.45	$222.40
Purchase #6	$167.75	8.778%	$182.4751	$182.48	$182.50	$182.50
Purchase #7	$129.69	3.102%	$133.713	$133.71	$133.70	$133.70
7 purchase totals =	$940.14		$1,009.8388	$1,009.83	$1,009.85	$1,009.90