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	$169.96	12.842%	$191.7863	$191.79	$191.80	$191.80
Purchase #2	$215.61	11.722%	$240.8838	$240.88	$240.90	$240.90
Purchase #3	$70.36	3.193%	$72.6066	$72.61	$72.60	$72.60
Purchase #4	$59.29	4.195%	$61.7772	$61.78	$61.80	$61.80
Purchase #5	$114.58	12.156%	$128.5083	$128.51	$128.50	$128.50
Purchase #6	$236.59	3.495%	$244.8588	$244.86	$244.85	$244.90
Purchase #7	$178.67	9.609%	$195.8384	$195.84	$195.85	$195.80
7 purchase totals =	$1,045.06		$1,136.2594	$1,136.27	$1,136.30	$1,136.30