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	$130.74	10.393%	$144.3278	$144.33	$144.35	$144.30
Purchase #2	$160.92	12.732%	$181.4083	$181.41	$181.40	$181.40
Purchase #3	$59.95	13.185%	$67.8544	$67.85	$67.85	$67.90
Purchase #4	$235.96	7.621%	$253.9425	$253.94	$253.95	$253.90
Purchase #5	$143.59	8.363%	$155.5984	$155.60	$155.60	$155.60
Purchase #6	$242.66	13.564%	$275.5744	$275.57	$275.55	$275.60
Purchase #7	$54.39	4.440%	$56.8049	$56.80	$56.80	$56.80
7 purchase totals =	$1,028.21		$1,135.5107	$1,135.50	$1,135.50	$1,135.50