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	$224.67	12.459%	$252.6616	$252.66	$252.65	$252.70
Purchase #2	$41.65	13.592%	$47.3111	$47.31	$47.30	$47.30
Purchase #3	$81.77	11.426%	$91.113	$91.11	$91.10	$91.10
Purchase #4	$101.37	3.544%	$104.9626	$104.96	$104.95	$105.00
Purchase #5	$43.54	4.298%	$45.4113	$45.41	$45.40	$45.40
Purchase #6	$182.47	7.842%	$196.7793	$196.78	$196.80	$196.80
Purchase #7	$78.47	7.588%	$84.4243	$84.42	$84.40	$84.40
7 purchase totals =	$753.94		$822.6632	$822.65	$822.60	$822.70