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	$71.49	9.773%	$78.4767	$78.48	$78.50	$78.50
Purchase #2	$227.49	6.770%	$242.8911	$242.89	$242.90	$242.90
Purchase #3	$90.70	8.248%	$98.1809	$98.18	$98.20	$98.20
Purchase #4	$160.83	13.855%	$183.113	$183.11	$183.10	$183.10
Purchase #5	$68.91	13.419%	$78.157	$78.16	$78.15	$78.20
Purchase #6	$196.90	5.749%	$208.2198	$208.22	$208.20	$208.20
Purchase #7	$188.93	4.331%	$197.1126	$197.11	$197.10	$197.10
7 purchase totals =	$1,005.25		$1,086.1511	$1,086.15	$1,086.15	$1,086.20