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	$62.88	11.513%	$70.1194	$70.12	$70.10	$70.10
Purchase #2	$169.36	5.338%	$178.4004	$178.40	$178.40	$178.40
Purchase #3	$110.86	5.127%	$116.5438	$116.54	$116.55	$116.50
Purchase #4	$227.96	11.828%	$254.9231	$254.92	$254.90	$254.90
Purchase #5	$95.80	7.672%	$103.1498	$103.15	$103.15	$103.10
Purchase #6	$128.80	3.365%	$133.1341	$133.13	$133.15	$133.10
Purchase #7	$59.40	5.430%	$62.6254	$62.63	$62.65	$62.60
7 purchase totals =	$855.06		$918.8960	$918.89	$918.90	$918.70