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	$77.43	5.153%	$81.42	$81.42	$81.40	$81.40
Purchase #2	$245.50	13.790%	$279.3545	$279.35	$279.35	$279.40
Purchase #3	$40.72	4.450%	$42.532	$42.53	$42.55	$42.50
Purchase #4	$168.96	7.619%	$181.8331	$181.83	$181.85	$181.80
Purchase #5	$150.45	3.379%	$155.5337	$155.53	$155.55	$155.50
Purchase #6	$142.86	6.371%	$151.9616	$151.96	$151.95	$152.00
Purchase #7	$220.39	8.110%	$238.2636	$238.26	$238.25	$238.30
7 purchase totals =	$1,046.31		$1,130.8985	$1,130.88	$1,130.90	$1,130.90