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	$180.56	6.643%	$192.5546	$192.55	$192.55	$192.60
Purchase #2	$170.55	6.180%	$181.09	$181.09	$181.10	$181.10
Purchase #3	$102.35	11.700%	$114.325	$114.33	$114.35	$114.30
Purchase #4	$234.56	12.694%	$264.335	$264.34	$264.35	$264.30
Purchase #5	$170.85	5.123%	$179.6026	$179.60	$179.60	$179.60
Purchase #6	$53.48	12.857%	$60.3559	$60.36	$60.35	$60.40
Purchase #7	$178.28	10.219%	$196.4984	$196.50	$196.50	$196.50
7 purchase totals =	$1,090.63		$1,188.7615	$1,188.77	$1,188.80	$1,188.80