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	8.352%	$148.3989	$148.40	$148.40	$148.40
Purchase #2	$185.76	7.296%	$199.313	$199.31	$199.30	$199.30
Purchase #3	$20.54	5.214%	$21.611	$21.61	$21.60	$21.60
Purchase #4	$249.70	12.761%	$281.5642	$281.56	$281.55	$281.60
Purchase #5	$98.64	5.595%	$104.1589	$104.16	$104.15	$104.20
Purchase #6	$88.62	3.724%	$91.9202	$91.92	$91.90	$91.90
Purchase #7	$38.95	12.674%	$43.8865	$43.89	$43.90	$43.90
7 purchase totals =	$819.17		$890.8527	$890.85	$890.80	$890.90