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	$247.86	10.784%	$274.5892	$274.59	$274.60	$274.60
Purchase #2	$203.56	9.850%	$223.6107	$223.61	$223.60	$223.60
Purchase #3	$241.95	11.813%	$270.5316	$270.53	$270.55	$270.50
Purchase #4	$228.63	10.588%	$252.8373	$252.84	$252.85	$252.80
Purchase #5	$6.34	10.522%	$7.0071	$7.01	$7.00	$7.00
Purchase #6	$153.73	7.777%	$165.6856	$165.69	$165.70	$165.70
Purchase #7	$71.45	10.500%	$78.9523	$78.95	$78.95	$79.00
7 purchase totals =	$1,153.52		$1,273.2138	$1,273.22	$1,273.25	$1,273.20