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	$83.96	3.109%	$86.5703	$86.57	$86.55	$86.60
Purchase #2	$196.54	12.303%	$220.7203	$220.72	$220.70	$220.70
Purchase #3	$49.30	6.260%	$52.3862	$52.39	$52.40	$52.40
Purchase #4	$201.86	4.132%	$210.2009	$210.20	$210.20	$210.20
Purchase #5	$240.26	6.237%	$255.245	$255.25	$255.25	$255.20
Purchase #6	$91.68	9.654%	$100.5308	$100.53	$100.55	$100.50
Purchase #7	$42.61	6.634%	$45.4367	$45.44	$45.45	$45.40
7 purchase totals =	$906.21		$971.0902	$971.10	$971.10	$971.00