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	$77.65	7.285%	$83.3068	$83.31	$83.30	$83.30
Purchase #2	$168.62	7.567%	$181.3795	$181.38	$181.40	$181.40
Purchase #3	$44.89	13.225%	$50.8267	$50.83	$50.85	$50.80
Purchase #4	$87.81	3.123%	$90.5523	$90.55	$90.55	$90.60
Purchase #5	$225.46	7.853%	$243.1654	$243.17	$243.15	$243.20
Purchase #6	$56.28	3.263%	$58.1164	$58.12	$58.10	$58.10
Purchase #7	$103.66	9.314%	$113.3149	$113.31	$113.30	$113.30
7 purchase totals =	$764.37		$820.6620	$820.67	$820.65	$820.70