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	$79.90	3.274%	$82.5159	$82.52	$82.50	$82.50
Purchase #2	$53.80	3.415%	$55.6373	$55.64	$55.65	$55.60
Purchase #3	$241.44	6.861%	$258.0052	$258.01	$258.00	$258.00
Purchase #4	$116.83	5.857%	$123.6727	$123.67	$123.65	$123.70
Purchase #5	$17.67	5.480%	$18.6383	$18.64	$18.65	$18.60
Purchase #6	$68.89	4.380%	$71.9074	$71.91	$71.90	$71.90
Purchase #7	$73.30	4.780%	$76.8037	$76.80	$76.80	$76.80
7 purchase totals =	$651.83		$687.1805	$687.19	$687.15	$687.10