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	$42.89	6.732%	$45.7774	$45.78	$45.80	$45.80
Purchase #2	$156.31	12.514%	$175.8706	$175.87	$175.85	$175.90
Purchase #3	$88.93	6.387%	$94.61	$94.61	$94.60	$94.60
Purchase #4	$195.89	7.142%	$209.8805	$209.88	$209.90	$209.90
Purchase #5	$228.95	5.258%	$240.9882	$240.99	$241.00	$241.00
Purchase #6	$21.40	3.529%	$22.1552	$22.16	$22.15	$22.20
Purchase #7	$38.81	3.596%	$40.2056	$40.21	$40.20	$40.20
7 purchase totals =	$773.18		$829.4875	$829.50	$829.50	$829.60