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	$159.54	7.501%	$171.5071	$171.51	$171.50	$171.50
Purchase #2	$73.92	4.752%	$77.4327	$77.43	$77.45	$77.40
Purchase #3	$225.71	10.419%	$249.2267	$249.23	$249.25	$249.20
Purchase #4	$231.63	13.848%	$263.7061	$263.71	$263.70	$263.70
Purchase #5	$133.63	3.150%	$137.8393	$137.84	$137.85	$137.80
Purchase #6	$210.52	8.236%	$227.8584	$227.86	$227.85	$227.90
Purchase #7	$27.81	12.289%	$31.2276	$31.23	$31.25	$31.20
7 purchase totals =	$1,062.76		$1,158.7979	$1,158.81	$1,158.85	$1,158.70