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	$70.91	3.530%	$73.4131	$73.41	$73.40	$73.40
Purchase #2	$131.46	10.815%	$145.6774	$145.68	$145.70	$145.70
Purchase #3	$57.88	3.463%	$59.8844	$59.88	$59.90	$59.90
Purchase #4	$83.98	7.824%	$90.5506	$90.55	$90.55	$90.60
Purchase #5	$204.34	4.707%	$213.9583	$213.96	$213.95	$214.00
Purchase #6	$119.98	6.700%	$128.0187	$128.02	$128.00	$128.00
Purchase #7	$5.90	4.128%	$6.1436	$6.14	$6.15	$6.10
7 purchase totals =	$674.45		$717.6461	$717.64	$717.65	$717.70