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	$86.61	3.212%	$89.3919	$89.39	$89.40	$89.40
Purchase #2	$217.47	8.223%	$235.3526	$235.35	$235.35	$235.40
Purchase #3	$179.33	8.355%	$194.313	$194.31	$194.30	$194.30
Purchase #4	$22.48	10.138%	$24.759	$24.76	$24.75	$24.80
Purchase #5	$89.29	13.724%	$101.5442	$101.54	$101.55	$101.50
Purchase #6	$30.33	7.441%	$32.5869	$32.59	$32.60	$32.60
Purchase #7	$77.28	4.279%	$80.5868	$80.59	$80.60	$80.60
7 purchase totals =	$702.79		$758.5344	$758.53	$758.55	$758.60