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	$215.41	7.415%	$231.3827	$231.38	$231.40	$231.40
Purchase #2	$37.42	12.582%	$42.1282	$42.13	$42.15	$42.10
Purchase #3	$238.61	10.816%	$264.4181	$264.42	$264.40	$264.40
Purchase #4	$181.92	10.254%	$200.5741	$200.57	$200.55	$200.60
Purchase #5	$27.90	8.710%	$30.3301	$30.33	$30.35	$30.30
Purchase #6	$157.88	9.187%	$172.3844	$172.38	$172.40	$172.40
Purchase #7	$186.27	11.172%	$207.0801	$207.08	$207.10	$207.10
7 purchase totals =	$1,045.41		$1,148.2977	$1,148.29	$1,148.35	$1,148.30