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	$91.87	12.698%	$103.5357	$103.54	$103.55	$103.50
Purchase #2	$216.76	3.166%	$223.6226	$223.62	$223.60	$223.60
Purchase #3	$61.70	12.532%	$69.4322	$69.43	$69.45	$69.40
Purchase #4	$85.58	4.330%	$89.2856	$89.29	$89.30	$89.30
Purchase #5	$250.70	7.243%	$268.8582	$268.86	$268.85	$268.90
Purchase #6	$101.85	12.504%	$114.5853	$114.59	$114.60	$114.60
Purchase #7	$115.55	8.729%	$125.6364	$125.64	$125.65	$125.60
7 purchase totals =	$924.01		$994.9560	$994.97	$995.00	$994.90