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	$57.33	12.517%	$64.506	$64.51	$64.50	$64.50
Purchase #2	$35.26	7.869%	$38.0346	$38.03	$38.05	$38.00
Purchase #3	$81.74	9.365%	$89.395	$89.40	$89.40	$89.40
Purchase #4	$47.70	9.871%	$52.4085	$52.41	$52.40	$52.40
Purchase #5	$215.71	10.687%	$238.7629	$238.76	$238.75	$238.80
Purchase #6	$181.96	5.302%	$191.6075	$191.61	$191.60	$191.60
Purchase #7	$90.58	7.554%	$97.4224	$97.42	$97.40	$97.40
7 purchase totals =	$710.28		$772.1369	$772.14	$772.10	$772.10