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	$7.25	13.299%	$8.2142	$8.21	$8.20	$8.20
Purchase #2	$89.52	11.632%	$99.933	$99.93	$99.95	$99.90
Purchase #3	$54.56	10.585%	$60.3352	$60.34	$60.35	$60.30
Purchase #4	$98.41	12.564%	$110.7742	$110.77	$110.75	$110.80
Purchase #5	$247.31	10.586%	$273.4902	$273.49	$273.50	$273.50
Purchase #6	$81.76	4.111%	$85.1212	$85.12	$85.10	$85.10
Purchase #7	$139.99	4.805%	$146.7165	$146.72	$146.70	$146.70
7 purchase totals =	$718.80		$784.5845	$784.58	$784.55	$784.50