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	$64.51	10.394%	$71.2152	$71.22	$71.20	$71.20
Purchase #2	$78.54	5.209%	$82.6311	$82.63	$82.65	$82.60
Purchase #3	$147.68	9.501%	$161.7111	$161.71	$161.70	$161.70
Purchase #4	$122.48	4.459%	$127.9414	$127.94	$127.95	$127.90
Purchase #5	$150.48	3.121%	$155.1765	$155.18	$155.20	$155.20
Purchase #6	$37.50	12.732%	$42.2745	$42.27	$42.25	$42.30
Purchase #7	$28.96	10.299%	$31.9426	$31.94	$31.95	$31.90
7 purchase totals =	$630.15		$672.8924	$672.89	$672.90	$672.80