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	$51.67	12.103%	$57.9236	$57.92	$57.90	$57.90
Purchase #2	$82.40	10.157%	$90.7694	$90.77	$90.75	$90.80
Purchase #3	$42.73	5.234%	$44.9665	$44.97	$44.95	$45.00
Purchase #4	$90.43	4.260%	$94.2823	$94.28	$94.30	$94.30
Purchase #5	$58.94	3.184%	$60.8166	$60.82	$60.80	$60.80
Purchase #6	$31.98	12.360%	$35.9327	$35.93	$35.95	$35.90
Purchase #7	$228.61	6.242%	$242.8798	$242.88	$242.90	$242.90
7 purchase totals =	$586.76		$627.5709	$627.57	$627.55	$627.60