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	$34.32	10.368%	$37.8783	$37.88	$37.90	$37.90
Purchase #2	$34.66	9.514%	$37.9576	$37.96	$37.95	$38.00
Purchase #3	$213.77	5.504%	$225.5359	$225.54	$225.55	$225.50
Purchase #4	$23.40	4.528%	$24.4596	$24.46	$24.45	$24.50
Purchase #5	$52.63	3.238%	$54.3342	$54.33	$54.35	$54.30
Purchase #6	$237.59	11.415%	$264.7109	$264.71	$264.70	$264.70
Purchase #7	$203.70	9.560%	$223.1737	$223.17	$223.15	$223.20
7 purchase totals =	$800.07		$868.0502	$868.05	$868.05	$868.10