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	$79.61	6.313%	$84.6358	$84.64	$84.65	$84.60
Purchase #2	$243.48	4.230%	$253.7792	$253.78	$253.80	$253.80
Purchase #3	$209.77	9.114%	$228.8884	$228.89	$228.90	$228.90
Purchase #4	$132.32	9.204%	$144.4987	$144.50	$144.50	$144.50
Purchase #5	$95.57	3.696%	$99.1023	$99.10	$99.10	$99.10
Purchase #6	$169.88	12.532%	$191.1694	$191.17	$191.15	$191.20
Purchase #7	$213.46	3.256%	$220.4103	$220.41	$220.40	$220.40
7 purchase totals =	$1,144.09		$1,222.4841	$1,222.49	$1,222.50	$1,222.50