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	$28.78	13.251%	$32.5936	$32.59	$32.60	$32.60
Purchase #2	$223.72	10.354%	$246.884	$246.88	$246.90	$246.90
Purchase #3	$100.32	3.467%	$103.7981	$103.80	$103.80	$103.80
Purchase #4	$186.47	12.371%	$209.5382	$209.54	$209.55	$209.50
Purchase #5	$106.50	9.592%	$116.7155	$116.72	$116.70	$116.70
Purchase #6	$55.50	12.743%	$62.5724	$62.57	$62.55	$62.60
Purchase #7	$65.43	7.847%	$70.5643	$70.56	$70.55	$70.60
7 purchase totals =	$766.72		$842.6661	$842.66	$842.65	$842.70