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	$46.72	8.488%	$50.6856	$50.69	$50.70	$50.70
Purchase #2	$234.35	10.331%	$258.5607	$258.56	$258.55	$258.60
Purchase #3	$175.40	9.181%	$191.5035	$191.50	$191.50	$191.50
Purchase #4	$241.94	10.852%	$268.1953	$268.20	$268.20	$268.20
Purchase #5	$31.43	11.845%	$35.1529	$35.15	$35.15	$35.20
Purchase #6	$131.58	7.812%	$141.859	$141.86	$141.85	$141.90
Purchase #7	$232.95	5.412%	$245.5573	$245.56	$245.55	$245.60
7 purchase totals =	$1,094.37		$1,191.5143	$1,191.52	$1,191.50	$1,191.70