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	$51.84	11.528%	$57.8161	$57.82	$57.80	$57.80
Purchase #2	$35.66	4.391%	$37.2258	$37.23	$37.25	$37.20
Purchase #3	$217.39	9.716%	$238.5116	$238.51	$238.50	$238.50
Purchase #4	$120.98	13.652%	$137.4962	$137.50	$137.50	$137.50
Purchase #5	$165.26	3.421%	$170.9135	$170.91	$170.90	$170.90
Purchase #6	$139.28	9.726%	$152.8264	$152.83	$152.85	$152.80
Purchase #7	$65.40	9.146%	$71.3815	$71.38	$71.40	$71.40
7 purchase totals =	$795.81		$866.1711	$866.18	$866.20	$866.10