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	$101.70	8.570%	$110.4157	$110.42	$110.40	$110.40
Purchase #2	$80.52	9.376%	$88.0696	$88.07	$88.05	$88.10
Purchase #3	$172.39	5.409%	$181.7146	$181.71	$181.70	$181.70
Purchase #4	$63.34	13.404%	$71.8301	$71.83	$71.85	$71.80
Purchase #5	$183.93	7.863%	$198.3924	$198.39	$198.40	$198.40
Purchase #6	$231.88	3.765%	$240.6103	$240.61	$240.60	$240.60
Purchase #7	$187.53	11.603%	$209.2891	$209.29	$209.30	$209.30
7 purchase totals =	$1,021.29		$1,100.3218	$1,100.32	$1,100.30	$1,100.30