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	$56.58	7.378%	$60.7545	$60.75	$60.75	$60.80
Purchase #2	$207.70	11.655%	$231.9074	$231.91	$231.90	$231.90
Purchase #3	$64.54	13.140%	$73.0206	$73.02	$73.00	$73.00
Purchase #4	$134.27	12.675%	$151.2887	$151.29	$151.30	$151.30
Purchase #5	$194.58	5.803%	$205.8715	$205.87	$205.85	$205.90
Purchase #6	$140.30	7.507%	$150.8323	$150.83	$150.85	$150.80
Purchase #7	$85.62	4.872%	$89.7914	$89.79	$89.80	$89.80
7 purchase totals =	$883.59		$963.4664	$963.46	$963.45	$963.50