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	$117.46	8.380%	$127.3031	$127.30	$127.30	$127.30
Purchase #2	$246.75	3.517%	$255.4282	$255.43	$255.45	$255.40
Purchase #3	$125.76	11.391%	$140.0853	$140.09	$140.10	$140.10
Purchase #4	$49.92	6.420%	$53.1249	$53.12	$53.10	$53.10
Purchase #5	$239.29	6.687%	$255.2913	$255.29	$255.30	$255.30
Purchase #6	$180.35	13.829%	$205.2906	$205.29	$205.30	$205.30
Purchase #7	$80.96	13.495%	$91.8856	$91.89	$91.90	$91.90
7 purchase totals =	$1,040.49		$1,128.4090	$1,128.41	$1,128.45	$1,128.40