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	$35.87	12.298%	$40.2813	$40.28	$40.30	$40.30
Purchase #2	$155.66	7.719%	$167.6754	$167.68	$167.70	$167.70
Purchase #3	$171.70	9.572%	$188.1351	$188.14	$188.15	$188.10
Purchase #4	$216.88	3.786%	$225.0911	$225.09	$225.10	$225.10
Purchase #5	$231.43	9.454%	$253.3094	$253.31	$253.30	$253.30
Purchase #6	$92.41	3.154%	$95.3246	$95.32	$95.30	$95.30
Purchase #7	$103.90	9.802%	$114.0843	$114.08	$114.10	$114.10
7 purchase totals =	$1,007.85		$1,083.9012	$1,083.90	$1,083.95	$1,083.90