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	$50.32	9.623%	$55.1623	$55.16	$55.15	$55.20
Purchase #2	$91.65	8.787%	$99.7033	$99.70	$99.70	$99.70
Purchase #3	$177.71	10.473%	$196.3216	$196.32	$196.30	$196.30
Purchase #4	$169.78	4.747%	$177.8395	$177.84	$177.85	$177.80
Purchase #5	$85.31	13.643%	$96.9488	$96.95	$96.95	$96.90
Purchase #6	$155.61	6.857%	$166.2802	$166.28	$166.30	$166.30
Purchase #7	$139.41	4.419%	$145.5705	$145.57	$145.55	$145.60
7 purchase totals =	$869.79		$937.8262	$937.82	$937.80	$937.80