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	$78.61	13.192%	$88.9802	$88.98	$89.00	$89.00
Purchase #2	$239.25	3.770%	$248.2697	$248.27	$248.25	$248.30
Purchase #3	$187.46	10.610%	$207.3495	$207.35	$207.35	$207.30
Purchase #4	$43.64	4.380%	$45.5514	$45.55	$45.55	$45.60
Purchase #5	$55.83	5.285%	$58.7806	$58.78	$58.80	$58.80
Purchase #6	$150.72	11.412%	$167.9202	$167.92	$167.90	$167.90
Purchase #7	$180.45	12.828%	$203.5981	$203.60	$203.60	$203.60
7 purchase totals =	$935.96		$1,020.4497	$1,020.45	$1,020.45	$1,020.50