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	$136.98	4.302%	$142.8729	$142.87	$142.85	$142.90
Purchase #2	$236.45	11.774%	$264.2896	$264.29	$264.30	$264.30
Purchase #3	$184.51	13.721%	$209.8266	$209.83	$209.85	$209.80
Purchase #4	$174.71	3.674%	$181.1288	$181.13	$181.15	$181.10
Purchase #5	$158.69	13.710%	$180.4464	$180.45	$180.45	$180.40
Purchase #6	$211.76	8.685%	$230.1514	$230.15	$230.15	$230.20
Purchase #7	$38.31	10.419%	$42.3015	$42.30	$42.30	$42.30
7 purchase totals =	$1,141.41		$1,251.0172	$1,251.02	$1,251.05	$1,251.00