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	$250.57	12.213%	$281.1721	$281.17	$281.15	$281.20
Purchase #2	$26.59	3.301%	$27.4677	$27.47	$27.45	$27.50
Purchase #3	$139.71	4.708%	$146.2875	$146.29	$146.30	$146.30
Purchase #4	$184.69	7.690%	$198.8927	$198.89	$198.90	$198.90
Purchase #5	$228.50	4.377%	$238.5014	$238.50	$238.50	$238.50
Purchase #6	$236.59	13.220%	$267.8672	$267.87	$267.85	$267.90
Purchase #7	$238.46	4.161%	$248.3823	$248.38	$248.40	$248.40
7 purchase totals =	$1,305.11		$1,408.5709	$1,408.57	$1,408.55	$1,408.70