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	$89.90	11.739%	$100.4534	$100.45	$100.45	$100.50
Purchase #2	$65.30	11.429%	$72.7631	$72.76	$72.75	$72.80
Purchase #3	$37.36	13.385%	$42.3606	$42.36	$42.35	$42.40
Purchase #4	$207.54	9.732%	$227.7378	$227.74	$227.75	$227.70
Purchase #5	$183.63	3.180%	$189.4694	$189.47	$189.45	$189.50
Purchase #6	$161.71	12.469%	$181.8736	$181.87	$181.85	$181.90
Purchase #7	$209.99	5.493%	$221.5248	$221.52	$221.50	$221.50
7 purchase totals =	$955.43		$1,036.1827	$1,036.17	$1,036.10	$1,036.30