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	$82.51	9.571%	$90.407	$90.41	$90.40	$90.40
Purchase #2	$212.91	7.809%	$229.5361	$229.54	$229.55	$229.50
Purchase #3	$187.39	11.861%	$209.6163	$209.62	$209.60	$209.60
Purchase #4	$89.34	6.762%	$95.3812	$95.38	$95.40	$95.40
Purchase #5	$45.26	6.862%	$48.3657	$48.37	$48.35	$48.40
Purchase #6	$59.84	12.373%	$67.244	$67.24	$67.25	$67.20
Purchase #7	$154.29	10.359%	$170.2729	$170.27	$170.25	$170.30
7 purchase totals =	$831.54		$910.8232	$910.83	$910.80	$910.80