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	$99.40	3.183%	$102.5639	$102.56	$102.55	$102.60
Purchase #2	$173.50	3.254%	$179.1457	$179.15	$179.15	$179.10
Purchase #3	$80.28	11.652%	$89.6342	$89.63	$89.65	$89.60
Purchase #4	$21.58	6.201%	$22.9182	$22.92	$22.90	$22.90
Purchase #5	$235.74	12.819%	$265.9595	$265.96	$265.95	$266.00
Purchase #6	$39.74	4.582%	$41.5609	$41.56	$41.55	$41.60
Purchase #7	$216.86	11.829%	$242.5124	$242.51	$242.50	$242.50
7 purchase totals =	$867.10		$944.2948	$944.29	$944.25	$944.30