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	$175.54	6.690%	$187.2836	$187.28	$187.30	$187.30
Purchase #2	$109.58	6.646%	$116.8627	$116.86	$116.85	$116.90
Purchase #3	$136.76	4.482%	$142.8896	$142.89	$142.90	$142.90
Purchase #4	$6.65	11.670%	$7.4261	$7.43	$7.45	$7.40
Purchase #5	$169.97	10.384%	$187.6197	$187.62	$187.60	$187.60
Purchase #6	$123.48	13.462%	$140.1029	$140.10	$140.10	$140.10
Purchase #7	$89.62	12.849%	$101.1353	$101.14	$101.15	$101.10
7 purchase totals =	$811.60		$883.3199	$883.32	$883.35	$883.30