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	$38.27	10.723%	$42.3737	$42.37	$42.35	$42.40
Purchase #2	$204.92	4.401%	$213.9385	$213.94	$213.95	$213.90
Purchase #3	$249.25	13.496%	$282.8888	$282.89	$282.90	$282.90
Purchase #4	$28.79	3.322%	$29.7464	$29.75	$29.75	$29.70
Purchase #5	$23.30	5.520%	$24.5862	$24.59	$24.60	$24.60
Purchase #6	$104.91	3.344%	$108.4182	$108.42	$108.40	$108.40
Purchase #7	$84.63	6.738%	$90.3324	$90.33	$90.35	$90.30
7 purchase totals =	$734.07		$792.2842	$792.29	$792.30	$792.20