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	$180.67	4.296%	$188.4316	$188.43	$188.45	$188.40
Purchase #2	$199.74	10.837%	$221.3858	$221.39	$221.40	$221.40
Purchase #3	$32.44	13.317%	$36.76	$36.76	$36.75	$36.80
Purchase #4	$113.85	11.592%	$127.0475	$127.05	$127.05	$127.00
Purchase #5	$169.36	6.603%	$180.5428	$180.54	$180.55	$180.50
Purchase #6	$72.34	11.182%	$80.4291	$80.43	$80.45	$80.40
Purchase #7	$29.81	12.115%	$33.4215	$33.42	$33.40	$33.40
7 purchase totals =	$798.21		$868.0183	$868.02	$868.05	$867.90