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	$60.41	12.377%	$67.8869	$67.89	$67.90	$67.90
Purchase #2	$22.94	6.276%	$24.3797	$24.38	$24.40	$24.40
Purchase #3	$93.44	7.585%	$100.5274	$100.53	$100.55	$100.50
Purchase #4	$157.96	4.650%	$165.3051	$165.31	$165.30	$165.30
Purchase #5	$91.77	12.548%	$103.2853	$103.29	$103.30	$103.30
Purchase #6	$13.28	4.446%	$13.8704	$13.87	$13.85	$13.90
Purchase #7	$39.53	9.647%	$43.3435	$43.34	$43.35	$43.30
7 purchase totals =	$479.33		$518.5983	$518.61	$518.65	$518.60