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	$35.32	5.588%	$37.2937	$37.29	$37.30	$37.30
Purchase #2	$203.49	8.806%	$221.4093	$221.41	$221.40	$221.40
Purchase #3	$182.80	11.379%	$203.6008	$203.60	$203.60	$203.60
Purchase #4	$143.96	6.180%	$152.8567	$152.86	$152.85	$152.90
Purchase #5	$188.45	13.301%	$213.5157	$213.52	$213.50	$213.50
Purchase #6	$174.31	6.555%	$185.736	$185.74	$185.75	$185.70
Purchase #7	$205.71	4.549%	$215.0677	$215.07	$215.05	$215.10
7 purchase totals =	$1,134.04		$1,229.4799	$1,229.49	$1,229.45	$1,229.50