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	$44.78	12.765%	$50.4962	$50.50	$50.50	$50.50
Purchase #2	$126.48	3.666%	$131.1168	$131.12	$131.10	$131.10
Purchase #3	$120.96	6.462%	$128.7764	$128.78	$128.80	$128.80
Purchase #4	$246.74	8.267%	$267.138	$267.14	$267.15	$267.10
Purchase #5	$63.74	11.849%	$71.2926	$71.29	$71.30	$71.30
Purchase #6	$151.86	3.304%	$156.8775	$156.88	$156.90	$156.90
Purchase #7	$121.91	3.257%	$125.8806	$125.88	$125.90	$125.90
7 purchase totals =	$876.47		$931.5781	$931.59	$931.65	$931.60