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	$164.80	10.776%	$182.5588	$182.56	$182.55	$182.60
Purchase #2	$105.32	4.310%	$109.8593	$109.86	$109.85	$109.90
Purchase #3	$194.26	12.643%	$218.8203	$218.82	$218.80	$218.80
Purchase #4	$20.92	4.306%	$21.8208	$21.82	$21.80	$21.80
Purchase #5	$95.48	11.518%	$106.4774	$106.48	$106.50	$106.50
Purchase #6	$74.56	8.414%	$80.8335	$80.83	$80.85	$80.80
Purchase #7	$84.78	12.724%	$95.5674	$95.57	$95.55	$95.60
7 purchase totals =	$740.12		$815.9375	$815.94	$815.90	$816.00