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	$171.65	9.804%	$188.4786	$188.48	$188.50	$188.50
Purchase #2	$125.90	4.697%	$131.8135	$131.81	$131.80	$131.80
Purchase #3	$164.32	11.261%	$182.8241	$182.82	$182.80	$182.80
Purchase #4	$96.89	5.345%	$102.0688	$102.07	$102.05	$102.10
Purchase #5	$174.48	10.788%	$193.3029	$193.30	$193.30	$193.30
Purchase #6	$111.30	11.333%	$123.9136	$123.91	$123.90	$123.90
Purchase #7	$69.66	10.510%	$76.9813	$76.98	$77.00	$77.00
7 purchase totals =	$914.20		$999.3828	$999.37	$999.35	$999.40