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	$32.37	13.351%	$36.6917	$36.69	$36.70	$36.70
Purchase #2	$43.68	8.309%	$47.3094	$47.31	$47.30	$47.30
Purchase #3	$162.96	13.536%	$185.0183	$185.02	$185.00	$185.00
Purchase #4	$142.59	6.780%	$152.2576	$152.26	$152.25	$152.30
Purchase #5	$43.92	8.758%	$47.7665	$47.77	$47.75	$47.80
Purchase #6	$98.39	13.219%	$111.3962	$111.40	$111.40	$111.40
Purchase #7	$186.91	6.698%	$199.4292	$199.43	$199.45	$199.40
7 purchase totals =	$710.82		$779.8689	$779.88	$779.85	$779.90