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	$52.74	7.699%	$56.8005	$56.80	$56.80	$56.80
Purchase #2	$145.90	3.375%	$150.8241	$150.82	$150.80	$150.80
Purchase #3	$123.50	11.826%	$138.1051	$138.11	$138.10	$138.10
Purchase #4	$79.60	4.216%	$82.9559	$82.96	$82.95	$83.00
Purchase #5	$82.89	7.864%	$89.4085	$89.41	$89.40	$89.40
Purchase #6	$169.87	10.460%	$187.6384	$187.64	$187.65	$187.60
Purchase #7	$164.26	3.483%	$169.9812	$169.98	$170.00	$170.00
7 purchase totals =	$818.76		$875.7137	$875.72	$875.70	$875.70