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	$85.39	5.314%	$89.9276	$89.93	$89.95	$89.90
Purchase #2	$201.73	8.289%	$218.4514	$218.45	$218.45	$218.50
Purchase #3	$67.29	13.830%	$76.5962	$76.60	$76.60	$76.60
Purchase #4	$73.74	12.758%	$83.1477	$83.15	$83.15	$83.10
Purchase #5	$38.89	5.147%	$40.8917	$40.89	$40.90	$40.90
Purchase #6	$51.56	9.302%	$56.3561	$56.36	$56.35	$56.40
Purchase #7	$55.36	5.264%	$58.2742	$58.27	$58.25	$58.30
7 purchase totals =	$573.96		$623.6449	$623.65	$623.65	$623.70