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	$56.48	3.839%	$58.6483	$58.65	$58.65	$58.60
Purchase #2	$85.64	5.280%	$90.1618	$90.16	$90.15	$90.20
Purchase #3	$202.60	12.657%	$228.2431	$228.24	$228.25	$228.20
Purchase #4	$234.84	4.502%	$245.4125	$245.41	$245.40	$245.40
Purchase #5	$177.89	11.455%	$198.2673	$198.27	$198.25	$198.30
Purchase #6	$120.55	9.543%	$132.0541	$132.05	$132.05	$132.10
Purchase #7	$245.83	9.556%	$269.3215	$269.32	$269.30	$269.30
7 purchase totals =	$1,123.83		$1,222.1086	$1,222.10	$1,222.05	$1,222.10