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	$80.54	10.712%	$89.1674	$89.17	$89.15	$89.20
Purchase #2	$82.58	7.142%	$88.4779	$88.48	$88.50	$88.50
Purchase #3	$121.41	6.321%	$129.0843	$129.08	$129.10	$129.10
Purchase #4	$6.86	10.276%	$7.5649	$7.56	$7.55	$7.60
Purchase #5	$170.48	10.166%	$187.811	$187.81	$187.80	$187.80
Purchase #6	$159.29	10.789%	$176.4758	$176.48	$176.50	$176.50
Purchase #7	$122.40	11.118%	$136.0084	$136.01	$136.00	$136.00
7 purchase totals =	$743.56		$814.5897	$814.59	$814.60	$814.70