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	$66.36	11.357%	$73.8965	$73.90	$73.90	$73.90
Purchase #2	$100.71	3.360%	$104.0939	$104.09	$104.10	$104.10
Purchase #3	$85.82	6.631%	$91.5107	$91.51	$91.50	$91.50
Purchase #4	$175.27	5.854%	$185.5303	$185.53	$185.55	$185.50
Purchase #5	$54.89	9.839%	$60.2906	$60.29	$60.30	$60.30
Purchase #6	$168.96	13.107%	$191.1056	$191.11	$191.10	$191.10
Purchase #7	$143.62	13.212%	$162.5951	$162.60	$162.60	$162.60
7 purchase totals =	$795.63		$869.0227	$869.03	$869.05	$869.00