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	$88.70	13.341%	$100.5335	$100.53	$100.55	$100.50
Purchase #2	$88.54	9.291%	$96.7663	$96.77	$96.75	$96.80
Purchase #3	$81.25	10.839%	$90.0567	$90.06	$90.05	$90.10
Purchase #4	$82.46	12.586%	$92.8384	$92.84	$92.85	$92.80
Purchase #5	$6.45	4.141%	$6.7171	$6.72	$6.70	$6.70
Purchase #6	$184.45	13.655%	$209.6366	$209.64	$209.65	$209.60
Purchase #7	$174.43	6.787%	$186.2686	$186.27	$186.25	$186.30
7 purchase totals =	$706.28		$782.8172	$782.83	$782.80	$782.80