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	$115.57	11.119%	$128.4202	$128.42	$128.40	$128.40
Purchase #2	$159.79	9.687%	$175.2689	$175.27	$175.25	$175.30
Purchase #3	$119.31	4.187%	$124.3055	$124.31	$124.30	$124.30
Purchase #4	$198.54	7.787%	$214.0003	$214.00	$214.00	$214.00
Purchase #5	$208.76	3.725%	$216.5363	$216.54	$216.55	$216.50
Purchase #6	$62.66	7.602%	$67.4234	$67.42	$67.40	$67.40
Purchase #7	$85.54	9.347%	$93.5354	$93.54	$93.55	$93.50
7 purchase totals =	$950.17		$1,019.4900	$1,019.50	$1,019.45	$1,019.40