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	$77.31	10.245%	$85.2304	$85.23	$85.25	$85.20
Purchase #2	$162.81	6.289%	$173.0491	$173.05	$173.05	$173.00
Purchase #3	$209.72	3.314%	$216.6701	$216.67	$216.65	$216.70
Purchase #4	$18.28	12.112%	$20.4941	$20.49	$20.50	$20.50
Purchase #5	$87.52	12.325%	$98.3068	$98.31	$98.30	$98.30
Purchase #6	$95.91	3.313%	$99.0875	$99.09	$99.10	$99.10
Purchase #7	$92.46	4.183%	$96.3276	$96.33	$96.35	$96.30
7 purchase totals =	$744.01		$789.1656	$789.17	$789.20	$789.10