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	$120.84	8.486%	$131.0945	$131.09	$131.10	$131.10
Purchase #2	$53.49	5.176%	$56.2586	$56.26	$56.25	$56.30
Purchase #3	$85.91	4.687%	$89.9366	$89.94	$89.95	$89.90
Purchase #4	$113.37	7.827%	$122.2435	$122.24	$122.25	$122.20
Purchase #5	$196.97	12.828%	$222.2373	$222.24	$222.25	$222.20
Purchase #6	$150.71	13.515%	$171.0785	$171.08	$171.10	$171.10
Purchase #7	$198.68	4.848%	$208.312	$208.31	$208.30	$208.30
7 purchase totals =	$919.97		$1,001.1610	$1,001.16	$1,001.20	$1,001.10