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	$92.60	6.346%	$98.4764	$98.48	$98.50	$98.50
Purchase #2	$142.91	11.344%	$159.1217	$159.12	$159.10	$159.10
Purchase #3	$54.83	9.254%	$59.904	$59.90	$59.90	$59.90
Purchase #4	$161.87	3.788%	$168.0016	$168.00	$168.00	$168.00
Purchase #5	$127.41	11.439%	$141.9844	$141.98	$142.00	$142.00
Purchase #6	$213.41	12.520%	$240.1289	$240.13	$240.15	$240.10
Purchase #7	$30.38	4.382%	$31.7113	$31.71	$31.70	$31.70
7 purchase totals =	$823.41		$899.3283	$899.32	$899.35	$899.30