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	$227.54	13.393%	$258.0144	$258.01	$258.00	$258.00
Purchase #2	$40.84	10.440%	$45.1037	$45.10	$45.10	$45.10
Purchase #3	$214.64	13.311%	$243.2107	$243.21	$243.20	$243.20
Purchase #4	$238.84	13.271%	$270.5365	$270.54	$270.55	$270.50
Purchase #5	$93.54	13.178%	$105.8667	$105.87	$105.85	$105.90
Purchase #6	$23.71	7.174%	$25.411	$25.41	$25.40	$25.40
Purchase #7	$149.78	12.279%	$168.1715	$168.17	$168.15	$168.20
7 purchase totals =	$988.89		$1,116.3145	$1,116.31	$1,116.25	$1,116.30