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	$112.45	7.548%	$120.9377	$120.94	$120.95	$120.90
Purchase #2	$31.57	4.767%	$33.0749	$33.07	$33.05	$33.10
Purchase #3	$148.69	9.499%	$162.8141	$162.81	$162.80	$162.80
Purchase #4	$28.48	13.141%	$32.2226	$32.22	$32.20	$32.20
Purchase #5	$141.98	9.392%	$155.3148	$155.31	$155.30	$155.30
Purchase #6	$48.84	11.739%	$54.5733	$54.57	$54.55	$54.60
Purchase #7	$63.25	13.744%	$71.9431	$71.94	$71.95	$71.90
7 purchase totals =	$575.26		$630.8805	$630.86	$630.80	$630.80