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	$82.46	8.673%	$89.6118	$89.61	$89.60	$89.60
Purchase #2	$233.51	11.524%	$260.4197	$260.42	$260.40	$260.40
Purchase #3	$125.45	7.248%	$134.5426	$134.54	$134.55	$134.50
Purchase #4	$149.91	13.699%	$170.4462	$170.45	$170.45	$170.40
Purchase #5	$20.95	11.180%	$23.2922	$23.29	$23.30	$23.30
Purchase #6	$193.86	11.736%	$216.6114	$216.61	$216.60	$216.60
Purchase #7	$99.51	9.582%	$109.045	$109.05	$109.05	$109.00
7 purchase totals =	$905.65		$1,003.9689	$1,003.97	$1,003.95	$1,003.80