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	$82.90	6.241%	$88.0738	$88.07	$88.05	$88.10
Purchase #2	$234.42	12.724%	$264.2476	$264.25	$264.25	$264.20
Purchase #3	$34.56	10.237%	$38.0979	$38.10	$38.10	$38.10
Purchase #4	$84.96	6.146%	$90.1816	$90.18	$90.20	$90.20
Purchase #5	$67.36	12.836%	$76.0063	$76.01	$76.00	$76.00
Purchase #6	$213.29	11.857%	$238.5798	$238.58	$238.60	$238.60
Purchase #7	$39.93	6.673%	$42.5945	$42.59	$42.60	$42.60
7 purchase totals =	$757.42		$837.7815	$837.78	$837.80	$837.80