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	$80.55	3.517%	$83.3829	$83.38	$83.40	$83.40
Purchase #2	$86.65	6.801%	$92.5431	$92.54	$92.55	$92.50
Purchase #3	$51.27	6.394%	$54.5482	$54.55	$54.55	$54.50
Purchase #4	$14.35	7.372%	$15.4079	$15.41	$15.40	$15.40
Purchase #5	$217.91	7.605%	$234.4821	$234.48	$234.50	$234.50
Purchase #6	$127.26	4.767%	$133.3265	$133.33	$133.35	$133.30
Purchase #7	$116.56	7.147%	$124.8905	$124.89	$124.90	$124.90
7 purchase totals =	$694.55		$738.5812	$738.58	$738.65	$738.50