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	$245.57	3.863%	$255.0564	$255.06	$255.05	$255.10
Purchase #2	$189.27	7.535%	$203.5315	$203.53	$203.55	$203.50
Purchase #3	$226.59	4.382%	$236.5192	$236.52	$236.50	$236.50
Purchase #4	$93.68	8.740%	$101.8676	$101.87	$101.85	$101.90
Purchase #5	$38.45	9.531%	$42.1147	$42.11	$42.10	$42.10
Purchase #6	$60.44	11.873%	$67.616	$67.62	$67.60	$67.60
Purchase #7	$50.62	5.614%	$53.4618	$53.46	$53.45	$53.50
7 purchase totals =	$904.62		$960.1672	$960.17	$960.10	$960.20