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	$79.88	11.525%	$89.0862	$89.09	$89.10	$89.10
Purchase #2	$54.98	12.566%	$61.8888	$61.89	$61.90	$61.90
Purchase #3	$95.37	4.307%	$99.4776	$99.48	$99.50	$99.50
Purchase #4	$144.45	10.403%	$159.4771	$159.48	$159.50	$159.50
Purchase #5	$80.54	10.247%	$88.7929	$88.79	$88.80	$88.80
Purchase #6	$237.99	11.299%	$264.8805	$264.88	$264.90	$264.90
Purchase #7	$25.50	10.353%	$28.14	$28.14	$28.15	$28.10
7 purchase totals =	$718.71		$791.7431	$791.75	$791.85	$791.80