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	$55.62	5.874%	$58.8871	$58.89	$58.90	$58.90
Purchase #2	$229.92	3.751%	$238.5443	$238.54	$238.55	$238.50
Purchase #3	$164.38	9.459%	$179.9287	$179.93	$179.95	$179.90
Purchase #4	$30.77	9.432%	$33.6722	$33.67	$33.65	$33.70
Purchase #5	$176.78	4.823%	$185.3061	$185.31	$185.30	$185.30
Purchase #6	$136.51	3.685%	$141.5404	$141.54	$141.55	$141.50
Purchase #7	$190.64	7.303%	$204.5624	$204.56	$204.55	$204.60
7 purchase totals =	$984.62		$1,042.4412	$1,042.44	$1,042.45	$1,042.40