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	$170.73	4.819%	$178.9575	$178.96	$178.95	$179.00
Purchase #2	$54.75	12.423%	$61.5516	$61.55	$61.55	$61.60
Purchase #3	$116.96	4.731%	$122.4934	$122.49	$122.50	$122.50
Purchase #4	$126.56	3.425%	$130.8947	$130.89	$130.90	$130.90
Purchase #5	$64.59	8.842%	$70.301	$70.30	$70.30	$70.30
Purchase #6	$162.88	3.613%	$168.7649	$168.76	$168.75	$168.80
Purchase #7	$126.35	12.194%	$141.7571	$141.76	$141.75	$141.80
7 purchase totals =	$822.82		$874.7202	$874.71	$874.70	$874.90