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	$40.87	4.329%	$42.6393	$42.64	$42.65	$42.60
Purchase #2	$240.45	4.328%	$250.8567	$250.86	$250.85	$250.90
Purchase #3	$30.67	12.479%	$34.4973	$34.50	$34.50	$34.50
Purchase #4	$24.26	8.334%	$26.2818	$26.28	$26.30	$26.30
Purchase #5	$153.61	13.665%	$174.6008	$174.60	$174.60	$174.60
Purchase #6	$193.89	10.306%	$213.8723	$213.87	$213.85	$213.90
Purchase #7	$64.50	10.648%	$71.368	$71.37	$71.35	$71.40
7 purchase totals =	$748.25		$814.1162	$814.12	$814.10	$814.20