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	$42.72	6.865%	$45.6527	$45.65	$45.65	$45.70
Purchase #2	$101.92	6.296%	$108.3369	$108.34	$108.35	$108.30
Purchase #3	$234.96	6.635%	$250.5496	$250.55	$250.55	$250.50
Purchase #4	$229.42	10.321%	$253.0984	$253.10	$253.10	$253.10
Purchase #5	$124.62	13.728%	$141.7278	$141.73	$141.75	$141.70
Purchase #6	$61.59	6.726%	$65.7325	$65.73	$65.75	$65.70
Purchase #7	$122.82	13.413%	$139.2938	$139.29	$139.30	$139.30
7 purchase totals =	$918.05		$1,004.3917	$1,004.39	$1,004.45	$1,004.30