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	$84.39	5.576%	$89.0956	$89.10	$89.10	$89.10
Purchase #2	$249.67	7.683%	$268.8521	$268.85	$268.85	$268.90
Purchase #3	$59.30	5.509%	$62.5668	$62.57	$62.55	$62.60
Purchase #4	$181.54	12.457%	$204.1544	$204.15	$204.15	$204.20
Purchase #5	$97.30	10.677%	$107.6887	$107.69	$107.70	$107.70
Purchase #6	$78.78	4.279%	$82.151	$82.15	$82.15	$82.20
Purchase #7	$38.35	12.569%	$43.1702	$43.17	$43.15	$43.20
7 purchase totals =	$789.33		$857.6788	$857.68	$857.65	$857.90