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	$102.46	9.416%	$112.1076	$112.11	$112.10	$112.10
Purchase #2	$205.35	12.419%	$230.8524	$230.85	$230.85	$230.90
Purchase #3	$235.76	9.592%	$258.3741	$258.37	$258.35	$258.40
Purchase #4	$53.53	11.232%	$59.5425	$59.54	$59.55	$59.50
Purchase #5	$105.71	6.643%	$112.7323	$112.73	$112.75	$112.70
Purchase #6	$116.47	12.786%	$131.3619	$131.36	$131.35	$131.40
Purchase #7	$208.50	13.280%	$236.1888	$236.19	$236.20	$236.20
7 purchase totals =	$1,027.78		$1,141.1596	$1,141.15	$1,141.15	$1,141.20