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	$7.62	11.451%	$8.4926	$8.49	$8.50	$8.50
Purchase #2	$216.40	8.113%	$233.9565	$233.96	$233.95	$234.00
Purchase #3	$42.52	11.464%	$47.3945	$47.39	$47.40	$47.40
Purchase #4	$119.25	6.510%	$127.0132	$127.01	$127.00	$127.00
Purchase #5	$239.72	7.670%	$258.1065	$258.11	$258.10	$258.10
Purchase #6	$159.76	3.562%	$165.4507	$165.45	$165.45	$165.50
Purchase #7	$33.36	11.280%	$37.123	$37.12	$37.10	$37.10
7 purchase totals =	$818.63		$877.5370	$877.53	$877.50	$877.60