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	$140.43	3.644%	$145.5473	$145.55	$145.55	$145.50
Purchase #2	$221.96	7.357%	$238.2896	$238.29	$238.30	$238.30
Purchase #3	$37.63	3.344%	$38.8883	$38.89	$38.90	$38.90
Purchase #4	$143.61	6.273%	$152.6187	$152.62	$152.60	$152.60
Purchase #5	$71.61	12.175%	$80.3285	$80.33	$80.35	$80.30
Purchase #6	$138.28	13.351%	$156.7418	$156.74	$156.75	$156.70
Purchase #7	$168.39	11.692%	$188.0782	$188.08	$188.10	$188.10
7 purchase totals =	$921.91		$1,000.4924	$1,000.50	$1,000.55	$1,000.40