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	$172.38	9.796%	$189.2663	$189.27	$189.25	$189.30
Purchase #2	$90.36	6.365%	$96.1114	$96.11	$96.10	$96.10
Purchase #3	$115.62	10.331%	$127.5647	$127.56	$127.55	$127.60
Purchase #4	$156.25	11.603%	$174.3797	$174.38	$174.40	$174.40
Purchase #5	$236.98	7.642%	$255.09	$255.09	$255.10	$255.10
Purchase #6	$14.37	9.741%	$15.7698	$15.77	$15.75	$15.80
Purchase #7	$47.76	5.238%	$50.2617	$50.26	$50.25	$50.30
7 purchase totals =	$833.72		$908.4436	$908.44	$908.40	$908.60