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	$35.97	5.329%	$37.8868	$37.89	$37.90	$37.90
Purchase #2	$18.75	12.743%	$21.1393	$21.14	$21.15	$21.10
Purchase #3	$95.99	3.517%	$99.366	$99.37	$99.35	$99.40
Purchase #4	$221.54	9.584%	$242.7724	$242.77	$242.75	$242.80
Purchase #5	$210.49	5.588%	$222.2522	$222.25	$222.25	$222.30
Purchase #6	$180.68	13.327%	$204.7592	$204.76	$204.75	$204.80
Purchase #7	$167.64	13.208%	$189.7819	$189.78	$189.80	$189.80
7 purchase totals =	$931.06		$1,017.9578	$1,017.96	$1,017.95	$1,018.10