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	$148.51	11.610%	$165.752	$165.75	$165.75	$165.80
Purchase #2	$189.49	4.641%	$198.2842	$198.28	$198.30	$198.30
Purchase #3	$244.89	8.560%	$265.8526	$265.85	$265.85	$265.90
Purchase #4	$139.33	10.594%	$154.0906	$154.09	$154.10	$154.10
Purchase #5	$210.76	6.242%	$223.9156	$223.92	$223.90	$223.90
Purchase #6	$93.79	6.142%	$99.5506	$99.55	$99.55	$99.60
Purchase #7	$21.76	9.604%	$23.8498	$23.85	$23.85	$23.80
7 purchase totals =	$1,048.53		$1,131.2954	$1,131.29	$1,131.30	$1,131.40