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	$101.36	13.595%	$115.1399	$115.14	$115.15	$115.10
Purchase #2	$204.64	9.383%	$223.8414	$223.84	$223.85	$223.80
Purchase #3	$166.54	11.592%	$185.8453	$185.85	$185.85	$185.80
Purchase #4	$147.29	3.384%	$152.2743	$152.27	$152.25	$152.30
Purchase #5	$242.45	9.164%	$264.6681	$264.67	$264.65	$264.70
Purchase #6	$108.89	8.542%	$118.1914	$118.19	$118.20	$118.20
Purchase #7	$171.93	6.213%	$182.612	$182.61	$182.60	$182.60
7 purchase totals =	$1,143.10		$1,242.5724	$1,242.57	$1,242.55	$1,242.50