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	$228.61	11.796%	$255.5768	$255.58	$255.60	$255.60
Purchase #2	$129.40	5.514%	$136.5351	$136.54	$136.55	$136.50
Purchase #3	$65.88	7.220%	$70.6365	$70.64	$70.65	$70.60
Purchase #4	$22.56	9.311%	$24.6606	$24.66	$24.65	$24.70
Purchase #5	$27.98	13.123%	$31.6518	$31.65	$31.65	$31.70
Purchase #6	$205.65	11.779%	$229.8735	$229.87	$229.85	$229.90
Purchase #7	$52.67	13.630%	$59.8489	$59.85	$59.85	$59.80
7 purchase totals =	$732.75		$808.7832	$808.79	$808.80	$808.80