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	$97.91	5.770%	$103.5594	$103.56	$103.55	$103.60
Purchase #2	$162.36	10.781%	$179.864	$179.86	$179.85	$179.90
Purchase #3	$92.95	6.218%	$98.7296	$98.73	$98.75	$98.70
Purchase #4	$40.32	6.263%	$42.8452	$42.85	$42.85	$42.80
Purchase #5	$161.48	10.335%	$178.169	$178.17	$178.15	$178.20
Purchase #6	$44.54	5.135%	$46.8271	$46.83	$46.85	$46.80
Purchase #7	$81.35	11.107%	$90.3855	$90.39	$90.40	$90.40
7 purchase totals =	$680.91		$740.3798	$740.39	$740.40	$740.40