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	$189.72	7.646%	$204.226	$204.23	$204.25	$204.20
Purchase #2	$162.61	6.399%	$173.0154	$173.02	$173.00	$173.00
Purchase #3	$46.28	5.662%	$48.9004	$48.90	$48.90	$48.90
Purchase #4	$222.76	11.684%	$248.7873	$248.79	$248.80	$248.80
Purchase #5	$89.96	11.614%	$100.408	$100.41	$100.40	$100.40
Purchase #6	$106.47	9.289%	$116.36	$116.36	$116.35	$116.40
Purchase #7	$42.67	9.703%	$46.8103	$46.81	$46.80	$46.80
7 purchase totals =	$860.47		$938.5074	$938.52	$938.50	$938.50