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	$117.83	8.836%	$128.2415	$128.24	$128.25	$128.20
Purchase #2	$75.48	8.650%	$82.009	$82.01	$82.00	$82.00
Purchase #3	$89.78	11.391%	$100.0068	$100.01	$100.00	$100.00
Purchase #4	$68.32	11.289%	$76.0326	$76.03	$76.05	$76.00
Purchase #5	$29.89	5.517%	$31.539	$31.54	$31.55	$31.50
Purchase #6	$111.41	3.528%	$115.3405	$115.34	$115.35	$115.30
Purchase #7	$93.67	11.505%	$104.4467	$104.45	$104.45	$104.40
7 purchase totals =	$586.38		$637.6161	$637.62	$637.65	$637.40