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	$45.28	11.130%	$50.3197	$50.32	$50.30	$50.30
Purchase #2	$213.33	4.738%	$223.4376	$223.44	$223.45	$223.40
Purchase #3	$168.60	10.239%	$185.863	$185.86	$185.85	$185.90
Purchase #4	$188.79	8.587%	$205.0014	$205.00	$205.00	$205.00
Purchase #5	$8.41	10.711%	$9.3108	$9.31	$9.30	$9.30
Purchase #6	$200.58	5.731%	$212.0752	$212.08	$212.10	$212.10
Purchase #7	$57.63	3.130%	$59.4338	$59.43	$59.45	$59.40
7 purchase totals =	$882.62		$945.4415	$945.44	$945.45	$945.40