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	$13.51	13.845%	$15.3805	$15.38	$15.40	$15.40
Purchase #2	$157.31	7.360%	$168.888	$168.89	$168.90	$168.90
Purchase #3	$54.41	9.593%	$59.6296	$59.63	$59.65	$59.60
Purchase #4	$224.62	5.478%	$236.9247	$236.92	$236.90	$236.90
Purchase #5	$128.73	7.301%	$138.1286	$138.13	$138.15	$138.10
Purchase #6	$148.93	5.793%	$157.5575	$157.56	$157.55	$157.60
Purchase #7	$222.32	3.290%	$229.6343	$229.63	$229.65	$229.60
7 purchase totals =	$949.83		$1,006.1432	$1,006.14	$1,006.20	$1,006.10