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	$180.78	4.721%	$189.3146	$189.31	$189.30	$189.30
Purchase #2	$169.44	4.349%	$176.8089	$176.81	$176.80	$176.80
Purchase #3	$176.39	3.314%	$182.2356	$182.24	$182.25	$182.20
Purchase #4	$81.82	8.108%	$88.454	$88.45	$88.45	$88.50
Purchase #5	$235.55	11.796%	$263.3355	$263.34	$263.35	$263.30
Purchase #6	$81.78	9.360%	$89.4346	$89.43	$89.45	$89.40
Purchase #7	$230.71	10.627%	$255.2276	$255.23	$255.25	$255.20
7 purchase totals =	$1,156.47		$1,244.8108	$1,244.81	$1,244.85	$1,244.70