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	$18.60	11.104%	$20.6653	$20.67	$20.65	$20.70
Purchase #2	$90.59	13.778%	$103.0715	$103.07	$103.05	$103.10
Purchase #3	$188.67	6.691%	$201.2939	$201.29	$201.30	$201.30
Purchase #4	$61.73	6.109%	$65.5011	$65.50	$65.50	$65.50
Purchase #5	$125.69	11.739%	$140.4447	$140.44	$140.45	$140.40
Purchase #6	$172.90	7.541%	$185.9384	$185.94	$185.95	$185.90
Purchase #7	$93.96	11.674%	$104.9289	$104.93	$104.95	$104.90
7 purchase totals =	$752.14		$821.8438	$821.84	$821.85	$821.80