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	$136.96	6.299%	$145.5871	$145.59	$145.60	$145.60
Purchase #2	$178.37	5.835%	$188.7779	$188.78	$188.80	$188.80
Purchase #3	$112.82	12.662%	$127.1053	$127.11	$127.10	$127.10
Purchase #4	$95.63	13.758%	$108.7868	$108.79	$108.80	$108.80
Purchase #5	$211.50	6.751%	$225.7784	$225.78	$225.80	$225.80
Purchase #6	$184.70	5.112%	$194.1419	$194.14	$194.15	$194.10
Purchase #7	$14.62	7.165%	$15.6675	$15.67	$15.65	$15.70
7 purchase totals =	$934.60		$1,005.8449	$1,005.86	$1,005.90	$1,005.90