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	$206.30	10.117%	$227.1714	$227.17	$227.15	$227.20
Purchase #2	$41.57	3.276%	$42.9318	$42.93	$42.95	$42.90
Purchase #3	$220.31	13.402%	$249.8359	$249.84	$249.85	$249.80
Purchase #4	$213.48	13.403%	$242.0927	$242.09	$242.10	$242.10
Purchase #5	$64.99	10.351%	$71.7171	$71.72	$71.70	$71.70
Purchase #6	$9.37	9.103%	$10.223	$10.22	$10.20	$10.20
Purchase #7	$128.94	6.605%	$137.4565	$137.46	$137.45	$137.50
7 purchase totals =	$884.96		$981.4284	$981.43	$981.40	$981.40