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	$222.97	7.540%	$239.7819	$239.78	$239.80	$239.80
Purchase #2	$188.36	10.382%	$207.9155	$207.92	$207.90	$207.90
Purchase #3	$78.32	4.780%	$82.0637	$82.06	$82.05	$82.10
Purchase #4	$47.76	5.815%	$50.5372	$50.54	$50.55	$50.50
Purchase #5	$56.46	8.626%	$61.3302	$61.33	$61.35	$61.30
Purchase #6	$39.39	11.391%	$43.8769	$43.88	$43.90	$43.90
Purchase #7	$56.28	6.466%	$59.9191	$59.92	$59.90	$59.90
7 purchase totals =	$689.54		$745.4245	$745.43	$745.45	$745.40