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	$98.93	4.434%	$103.3166	$103.32	$103.30	$103.30
Purchase #2	$53.84	10.629%	$59.5627	$59.56	$59.55	$59.60
Purchase #3	$249.39	10.326%	$275.142	$275.14	$275.15	$275.10
Purchase #4	$87.96	6.746%	$93.8938	$93.89	$93.90	$93.90
Purchase #5	$5.72	11.142%	$6.3573	$6.36	$6.35	$6.40
Purchase #6	$98.56	10.137%	$108.551	$108.55	$108.55	$108.60
Purchase #7	$112.29	12.227%	$126.0197	$126.02	$126.00	$126.00
7 purchase totals =	$706.69		$772.8431	$772.84	$772.80	$772.90