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	$171.82	5.221%	$180.7907	$180.79	$180.80	$180.80
Purchase #2	$106.89	12.302%	$120.0396	$120.04	$120.05	$120.00
Purchase #3	$99.28	13.243%	$112.4277	$112.43	$112.45	$112.40
Purchase #4	$64.45	12.118%	$72.2601	$72.26	$72.25	$72.30
Purchase #5	$192.76	3.793%	$200.0714	$200.07	$200.05	$200.10
Purchase #6	$96.80	12.179%	$108.5893	$108.59	$108.60	$108.60
Purchase #7	$162.59	6.104%	$172.5145	$172.51	$172.50	$172.50
7 purchase totals =	$894.59		$966.6933	$966.69	$966.70	$966.70