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	$87.82	13.111%	$99.3341	$99.33	$99.35	$99.30
Purchase #2	$28.34	9.412%	$31.0074	$31.01	$31.00	$31.00
Purchase #3	$86.76	11.392%	$96.6437	$96.64	$96.65	$96.60
Purchase #4	$79.60	13.483%	$90.3325	$90.33	$90.35	$90.30
Purchase #5	$242.46	11.705%	$270.8399	$270.84	$270.85	$270.80
Purchase #6	$229.42	9.626%	$251.504	$251.50	$251.50	$251.50
Purchase #7	$214.50	7.417%	$230.4095	$230.41	$230.40	$230.40
7 purchase totals =	$968.90		$1,070.0711	$1,070.06	$1,070.10	$1,069.90