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	$123.89	4.255%	$129.1615	$129.16	$129.15	$129.20
Purchase #2	$89.89	11.515%	$100.2408	$100.24	$100.25	$100.20
Purchase #3	$112.57	8.530%	$122.1722	$122.17	$122.15	$122.20
Purchase #4	$63.41	10.409%	$70.0103	$70.01	$70.00	$70.00
Purchase #5	$59.99	12.585%	$67.5397	$67.54	$67.55	$67.50
Purchase #6	$206.71	3.266%	$213.4611	$213.46	$213.45	$213.50
Purchase #7	$109.52	7.655%	$117.9038	$117.90	$117.90	$117.90
7 purchase totals =	$765.98		$820.4894	$820.48	$820.45	$820.50