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	$78.38	6.548%	$83.5123	$83.51	$83.50	$83.50
Purchase #2	$178.74	4.673%	$187.0925	$187.09	$187.10	$187.10
Purchase #3	$57.70	11.484%	$64.3263	$64.33	$64.35	$64.30
Purchase #4	$8.80	5.763%	$9.3071	$9.31	$9.30	$9.30
Purchase #5	$82.84	8.269%	$89.69	$89.69	$89.70	$89.70
Purchase #6	$87.73	3.396%	$90.7093	$90.71	$90.70	$90.70
Purchase #7	$67.61	4.649%	$70.7532	$70.75	$70.75	$70.80
7 purchase totals =	$561.80		$595.3907	$595.39	$595.40	$595.40