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	$5.88	12.682%	$6.6257	$6.63	$6.65	$6.60
Purchase #2	$136.36	10.843%	$151.1455	$151.15	$151.15	$151.10
Purchase #3	$147.30	10.405%	$162.6266	$162.63	$162.65	$162.60
Purchase #4	$144.30	9.870%	$158.5424	$158.54	$158.55	$158.50
Purchase #5	$186.45	4.190%	$194.2623	$194.26	$194.25	$194.30
Purchase #6	$65.29	10.553%	$72.1801	$72.18	$72.20	$72.20
Purchase #7	$181.35	8.555%	$196.8645	$196.86	$196.85	$196.90
7 purchase totals =	$866.93		$942.2471	$942.25	$942.30	$942.20