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	$32.96	10.501%	$36.4211	$36.42	$36.40	$36.40
Purchase #2	$235.26	12.604%	$264.9122	$264.91	$264.90	$264.90
Purchase #3	$135.42	5.408%	$142.7435	$142.74	$142.75	$142.70
Purchase #4	$196.41	13.494%	$222.9136	$222.91	$222.90	$222.90
Purchase #5	$29.35	12.706%	$33.0792	$33.08	$33.10	$33.10
Purchase #6	$62.26	11.366%	$69.3365	$69.34	$69.35	$69.30
Purchase #7	$128.81	11.377%	$143.4647	$143.46	$143.45	$143.50
7 purchase totals =	$820.47		$912.8708	$912.86	$912.85	$912.80