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	$65.44	11.371%	$72.8812	$72.88	$72.90	$72.90
Purchase #2	$80.42	9.617%	$88.154	$88.15	$88.15	$88.20
Purchase #3	$105.27	6.628%	$112.2473	$112.25	$112.25	$112.20
Purchase #4	$84.71	4.305%	$88.3568	$88.36	$88.35	$88.40
Purchase #5	$135.54	7.765%	$146.0647	$146.06	$146.05	$146.10
Purchase #6	$131.83	13.608%	$149.7694	$149.77	$149.75	$149.80
Purchase #7	$156.46	6.368%	$166.4234	$166.42	$166.40	$166.40
7 purchase totals =	$759.67		$823.8968	$823.89	$823.85	$824.00