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	$37.33	4.213%	$38.9027	$38.90	$38.90	$38.90
Purchase #2	$69.53	10.860%	$77.081	$77.08	$77.10	$77.10
Purchase #3	$100.54	12.241%	$112.8471	$112.85	$112.85	$112.80
Purchase #4	$199.65	8.537%	$216.6941	$216.69	$216.70	$216.70
Purchase #5	$142.33	7.560%	$153.0901	$153.09	$153.10	$153.10
Purchase #6	$15.59	3.345%	$16.1115	$16.11	$16.10	$16.10
Purchase #7	$49.32	5.709%	$52.1357	$52.14	$52.15	$52.10
7 purchase totals =	$614.29		$666.8622	$666.86	$666.90	$666.80