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	$217.78	7.137%	$233.323	$233.32	$233.30	$233.30
Purchase #2	$54.66	3.450%	$56.5458	$56.55	$56.55	$56.50
Purchase #3	$212.64	9.223%	$232.2518	$232.25	$232.25	$232.30
Purchase #4	$168.66	9.751%	$185.106	$185.11	$185.10	$185.10
Purchase #5	$63.33	6.731%	$67.5927	$67.59	$67.60	$67.60
Purchase #6	$13.51	12.394%	$15.1844	$15.18	$15.20	$15.20
Purchase #7	$80.38	10.748%	$89.0192	$89.02	$89.00	$89.00
7 purchase totals =	$810.96		$879.0229	$879.02	$879.00	$879.00