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	$142.41	12.334%	$159.9748	$159.97	$159.95	$160.00
Purchase #2	$38.61	9.502%	$42.2787	$42.28	$42.30	$42.30
Purchase #3	$250.78	7.355%	$269.2249	$269.22	$269.20	$269.20
Purchase #4	$111.30	7.284%	$119.4071	$119.41	$119.40	$119.40
Purchase #5	$49.96	10.849%	$55.3802	$55.38	$55.40	$55.40
Purchase #6	$110.62	11.314%	$123.1355	$123.14	$123.15	$123.10
Purchase #7	$83.88	7.292%	$89.9965	$90.00	$90.00	$90.00
7 purchase totals =	$787.56		$859.3977	$859.40	$859.40	$859.40