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	$170.79	10.803%	$189.2404	$189.24	$189.25	$189.20
Purchase #2	$29.96	6.758%	$31.9847	$31.98	$32.00	$32.00
Purchase #3	$95.56	10.410%	$105.5078	$105.51	$105.50	$105.50
Purchase #4	$246.63	10.703%	$273.0268	$273.03	$273.05	$273.00
Purchase #5	$83.26	8.469%	$90.3113	$90.31	$90.30	$90.30
Purchase #6	$82.77	7.722%	$89.1615	$89.16	$89.15	$89.20
Purchase #7	$105.30	9.340%	$115.135	$115.14	$115.15	$115.10
7 purchase totals =	$814.27		$894.3675	$894.37	$894.40	$894.30