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	$83.49	6.463%	$88.886	$88.89	$88.90	$88.90
Purchase #2	$61.43	13.317%	$69.6106	$69.61	$69.60	$69.60
Purchase #3	$121.28	5.513%	$127.9662	$127.97	$127.95	$128.00
Purchase #4	$240.58	9.847%	$264.2699	$264.27	$264.25	$264.30
Purchase #5	$244.64	11.654%	$273.1503	$273.15	$273.15	$273.20
Purchase #6	$52.63	8.676%	$57.1962	$57.20	$57.20	$57.20
Purchase #7	$78.92	13.873%	$89.8686	$89.87	$89.85	$89.90
7 purchase totals =	$882.97		$970.9478	$970.96	$970.90	$971.10