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	$37.29	13.197%	$42.2112	$42.21	$42.20	$42.20
Purchase #2	$113.74	4.176%	$118.4898	$118.49	$118.50	$118.50
Purchase #3	$155.39	6.289%	$165.1625	$165.16	$165.15	$165.20
Purchase #4	$242.82	6.804%	$259.3415	$259.34	$259.35	$259.30
Purchase #5	$134.69	5.103%	$141.5632	$141.56	$141.55	$141.60
Purchase #6	$212.41	4.302%	$221.5479	$221.55	$221.55	$221.50
Purchase #7	$201.59	10.676%	$223.1117	$223.11	$223.10	$223.10
7 purchase totals =	$1,097.93		$1,171.4278	$1,171.42	$1,171.40	$1,171.40