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	$34.60	13.497%	$39.27	$39.27	$39.25	$39.30
Purchase #2	$62.91	7.216%	$67.4496	$67.45	$67.45	$67.40
Purchase #3	$174.56	4.194%	$181.881	$181.88	$181.90	$181.90
Purchase #4	$225.40	10.810%	$249.7657	$249.77	$249.75	$249.80
Purchase #5	$160.36	8.849%	$174.5503	$174.55	$174.55	$174.60
Purchase #6	$118.41	4.871%	$124.1778	$124.18	$124.20	$124.20
Purchase #7	$60.54	11.241%	$67.3453	$67.35	$67.35	$67.30
7 purchase totals =	$836.78		$904.4397	$904.45	$904.45	$904.50