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	$203.78	12.818%	$229.9005	$229.90	$229.90	$229.90
Purchase #2	$233.92	6.802%	$249.8312	$249.83	$249.85	$249.80
Purchase #3	$114.47	7.740%	$123.33	$123.33	$123.35	$123.30
Purchase #4	$136.64	13.668%	$155.316	$155.32	$155.30	$155.30
Purchase #5	$131.84	10.445%	$145.6107	$145.61	$145.60	$145.60
Purchase #6	$211.77	12.477%	$238.1925	$238.19	$238.20	$238.20
Purchase #7	$31.61	8.179%	$34.1954	$34.20	$34.20	$34.20
7 purchase totals =	$1,064.03		$1,176.3763	$1,176.38	$1,176.40	$1,176.30