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	$17.88	11.268%	$19.8947	$19.89	$19.90	$19.90
Purchase #2	$19.45	5.203%	$20.462	$20.46	$20.45	$20.50
Purchase #3	$225.55	8.282%	$244.2301	$244.23	$244.25	$244.20
Purchase #4	$81.28	8.592%	$88.2636	$88.26	$88.25	$88.30
Purchase #5	$156.46	7.837%	$168.7218	$168.72	$168.70	$168.70
Purchase #6	$131.59	8.605%	$142.9133	$142.91	$142.90	$142.90
Purchase #7	$132.38	5.692%	$139.9151	$139.92	$139.90	$139.90
7 purchase totals =	$764.59		$824.4006	$824.39	$824.35	$824.40