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	$186.48	7.728%	$200.8912	$200.89	$200.90	$200.90
Purchase #2	$113.42	4.474%	$118.4944	$118.49	$118.50	$118.50
Purchase #3	$199.32	11.194%	$221.6319	$221.63	$221.65	$221.60
Purchase #4	$234.41	3.275%	$242.0869	$242.09	$242.10	$242.10
Purchase #5	$13.91	9.184%	$15.1875	$15.19	$15.20	$15.20
Purchase #6	$42.35	12.559%	$47.6687	$47.67	$47.65	$47.70
Purchase #7	$32.86	12.828%	$37.0753	$37.08	$37.10	$37.10
7 purchase totals =	$822.75		$883.0359	$883.04	$883.10	$883.10