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	$32.69	7.541%	$35.1552	$35.16	$35.15	$35.20
Purchase #2	$104.63	7.424%	$112.3977	$112.40	$112.40	$112.40
Purchase #3	$75.59	6.285%	$80.3408	$80.34	$80.35	$80.30
Purchase #4	$18.75	10.125%	$20.6484	$20.65	$20.65	$20.60
Purchase #5	$156.59	7.412%	$168.1965	$168.20	$168.20	$168.20
Purchase #6	$39.40	10.201%	$43.4192	$43.42	$43.40	$43.40
Purchase #7	$124.31	5.844%	$131.5747	$131.57	$131.55	$131.60
7 purchase totals =	$551.96		$591.7325	$591.74	$591.70	$591.70