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	$86.45	4.377%	$90.2339	$90.23	$90.25	$90.20
Purchase #2	$248.42	11.235%	$276.33	$276.33	$276.35	$276.30
Purchase #3	$155.70	11.174%	$173.0979	$173.10	$173.10	$173.10
Purchase #4	$202.90	10.258%	$223.7135	$223.71	$223.70	$223.70
Purchase #5	$78.85	10.823%	$87.3839	$87.38	$87.40	$87.40
Purchase #6	$12.36	9.483%	$13.5321	$13.53	$13.55	$13.50
Purchase #7	$218.67	4.554%	$228.6282	$228.63	$228.65	$228.60
7 purchase totals =	$1,003.35		$1,092.9195	$1,092.91	$1,093.00	$1,092.80