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	$66.25	10.191%	$73.0015	$73.00	$73.00	$73.00
Purchase #2	$187.85	4.662%	$196.6076	$196.61	$196.60	$196.60
Purchase #3	$29.42	13.199%	$33.3031	$33.30	$33.30	$33.30
Purchase #4	$142.94	6.118%	$151.6851	$151.69	$151.70	$151.70
Purchase #5	$39.36	6.678%	$41.9885	$41.99	$42.00	$42.00
Purchase #6	$85.51	7.676%	$92.0737	$92.07	$92.05	$92.10
Purchase #7	$243.43	3.133%	$251.0567	$251.06	$251.05	$251.10
7 purchase totals =	$794.76		$839.7162	$839.72	$839.70	$839.80