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	$235.28	6.519%	$250.6179	$250.62	$250.60	$250.60
Purchase #2	$28.43	9.761%	$31.2051	$31.21	$31.20	$31.20
Purchase #3	$36.88	7.609%	$39.6862	$39.69	$39.70	$39.70
Purchase #4	$103.96	5.307%	$109.4772	$109.48	$109.50	$109.50
Purchase #5	$28.90	11.191%	$32.1342	$32.13	$32.15	$32.10
Purchase #6	$165.70	13.281%	$187.7066	$187.71	$187.70	$187.70
Purchase #7	$50.80	13.629%	$57.7235	$57.72	$57.70	$57.70
7 purchase totals =	$649.95		$708.5507	$708.56	$708.55	$708.50