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	$115.79	7.226%	$124.157	$124.16	$124.15	$124.20
Purchase #2	$38.34	12.720%	$43.2168	$43.22	$43.20	$43.20
Purchase #3	$149.78	8.272%	$162.1698	$162.17	$162.15	$162.20
Purchase #4	$68.49	5.285%	$72.1097	$72.11	$72.10	$72.10
Purchase #5	$28.96	9.201%	$31.6246	$31.62	$31.60	$31.60
Purchase #6	$196.48	13.297%	$222.6059	$222.61	$222.60	$222.60
Purchase #7	$11.75	11.556%	$13.1078	$13.11	$13.10	$13.10
7 purchase totals =	$609.59		$668.9916	$669.00	$668.90	$669.00