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	$54.28	12.618%	$61.1291	$61.13	$61.15	$61.10
Purchase #2	$78.32	7.639%	$84.3029	$84.30	$84.30	$84.30
Purchase #3	$205.61	7.514%	$221.0595	$221.06	$221.05	$221.10
Purchase #4	$126.95	9.689%	$139.2502	$139.25	$139.25	$139.30
Purchase #5	$147.91	7.395%	$158.8479	$158.85	$158.85	$158.80
Purchase #6	$227.38	13.614%	$258.3355	$258.34	$258.35	$258.30
Purchase #7	$147.35	12.393%	$165.6111	$165.61	$165.60	$165.60
7 purchase totals =	$987.80		$1,088.5362	$1,088.54	$1,088.55	$1,088.50