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	$83.97	6.501%	$89.4289	$89.43	$89.45	$89.40
Purchase #2	$208.30	4.681%	$218.0505	$218.05	$218.05	$218.10
Purchase #3	$230.61	8.274%	$249.6907	$249.69	$249.70	$249.70
Purchase #4	$159.39	3.543%	$165.0372	$165.04	$165.05	$165.00
Purchase #5	$102.43	10.711%	$113.4013	$113.40	$113.40	$113.40
Purchase #6	$89.90	13.372%	$101.9214	$101.92	$101.90	$101.90
Purchase #7	$135.49	9.106%	$147.8277	$147.83	$147.85	$147.80
7 purchase totals =	$1,010.09		$1,085.3577	$1,085.36	$1,085.40	$1,085.30