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	$140.25	5.104%	$147.4084	$147.41	$147.40	$147.40
Purchase #2	$35.45	13.515%	$40.2411	$40.24	$40.25	$40.20
Purchase #3	$39.38	12.137%	$44.1596	$44.16	$44.15	$44.20
Purchase #4	$128.49	10.650%	$142.1742	$142.17	$142.15	$142.20
Purchase #5	$83.95	3.521%	$86.9059	$86.91	$86.90	$86.90
Purchase #6	$104.83	12.455%	$117.8866	$117.89	$117.90	$117.90
Purchase #7	$241.73	7.203%	$259.1418	$259.14	$259.15	$259.10
7 purchase totals =	$774.08		$837.9176	$837.92	$837.90	$837.90